PostgreSQL Database

PostgreSQL Database — Skill

Use this skill when working with PostgreSQL database in Delphi projects via FireDAC.

When to Use

• When configuring FireDAC connection with PostgreSQL
• When creating tables, sequences, functions, triggers and views
• When implementing Repositories with FireDAC + PostgreSQL
• When working with advanced types (JSONB, Arrays, UUID, ENUM)
• When implementing UPSERT, CTEs, Full-Text Search or Window Functions
• When planning schema migrations (versioned scripts)

PostgreSQL Versions

Recommendation: Use PostgreSQL 14+ for new projects. Enjoy MERGE, JSONB and partitioning.

FireDAC Connection with PostgreSQL

Minimum Configuration

unit MeuApp.Infra.Database.PostgreSQL.Connection;

interface

uses
  FireDAC.Comp.Client,
  FireDAC.Phys.PG,         //Driver PostgreSQL
  FireDAC.Phys.PGDef,      //Defaults do PostgreSQL
  FireDAC.Stan.Def,
  FireDAC.Stan.Pool,
  FireDAC.DApt;

type
  ///<summary>
  ///PostgreSQL connection factory via FireDAC.
  ///</summary>
  TPostgreSQLConnectionFactory = class
  public
    ///<summary>
    ///Creates and configures a PostgreSQL connection.
    ///</summary>
    ///<param name="AServer">Server address</param>
    ///<param name="ADatabase">Database name</param>
    ///<param name="AUserName">User (default: postgres)</param>
    ///<param name="APassword">Bank password</param>
    ///<param name="APort">Port (default: 5432)</param>
    ///<returns>FireDAC connection configured and opened</returns>
    class function CreateConnection(
      const AServer: string;
      const ADatabase: string;
      const AUserName: string = 'postgres';
      const APassword: string = '';
      APort: Integer = 5432
    ): TFDConnection;

    ///<summary>
    ///Creates connection via full connection string.
    ///</summary>
    class function CreateFromConnectionString(
      const AConnectionString: string
    ): TFDConnection;
  end;

implementation

uses
  System.SysUtils;

class function TPostgreSQLConnectionFactory.CreateConnection(
  const AServer, ADatabase, AUserName, APassword: string;
  APort: Integer): TFDConnection;
begin
  if ADatabase.Trim.IsEmpty then
    raise EArgumentException.Create('ADatabase não pode ser vazio');

  Result := TFDConnection.Create(nil);
  try
    Result.DriverName := 'PG';
    Result.Params.Values['Server'] := AServer;
    Result.Params.Values['Port'] := APort.ToString;
    Result.Params.Database := ADatabase;
    Result.Params.UserName := AUserName;
    Result.Params.Password := APassword;

    { Configurações recomendadas }
    Result.Params.Values['CharacterSet'] := 'UTF8';

    { Opções do driver FireDAC }
    Result.FormatOptions.StrsTrim2Len := True;
    Result.FetchOptions.Mode := fmAll;
    Result.ResourceOptions.AutoReconnect := True;
    Result.TxOptions.Isolation := xiReadCommitted;

    { Schema padrão — 'public' por default, alterar se necessário }
    //Result.Params.Values['MetaDefSchema'] := 'public';

    Result.Connected := True;
  except
    Result.Free;
    raise;
  end;
end;

class function TPostgreSQLConnectionFactory.CreateFromConnectionString(
  const AConnectionString: string): TFDConnection;
begin
  Result := TFDConnection.Create(nil);
  try
    Result.ConnectionString := AConnectionString;
    Result.Connected := True;
  except
    Result.Free;
    raise;
  end;
end;

FDPhysPGDriverLink — Configure Client Library

uses
  FireDAC.Phys.PGWrapper,
  FireDAC.Phys.PG;

var
  LDriverLink: TFDPhysPGDriverLink;
begin
  LDriverLink := TFDPhysPGDriverLink.Create(nil);
  try
    { Apontar libpq.dll customizado (32/64-bit) }
    LDriverLink.VendorLib := 'C:\PostgreSQL\bin\libpq.dll';

    { Windows: precisa também libintl-9.dll, libeay32.dll, ssleay32.dll no PATH }
  finally
    { DriverLink vive por toda a aplicação — criar no DataModule }
  end;
end;

Connection Pooling

{ Via FDManager }
FDManager.ConnectionDefs.AddConnectionDef;
with FDManager.ConnectionDefs.ConnectionDefByName('PG_POOL') do
begin
  DriverID := 'PG';
  Server := 'localhost';
  Port := 5432;
  Database := 'meubanco';
  UserName := 'postgres';
  Password := 'senha';
  Params.Values['CharacterSet'] := 'UTF8';
  Params.Values['Pooled'] := 'True';
  Params.Values['POOL_MaximumItems'] := '50';
  Params.Values['POOL_CleanupTimeout'] := '30000';
  Params.Values['POOL_ExpireTimeout'] := '90000';
end;

SSL/TLS

{ Conexão segura com SSL }
Result.Params.Values['PGAdvanced'] := 'sslmode=require';
{ Para certificado de cliente: }
//Result.Params.Values['PGAdvanced'] :=
//'sslmode=verify-full;sslcert=client-cert.pem;sslkey=client-key.pem;sslrootcert=ca.pem';

Data Types — PostgreSQL Mapping ↔ Delphi

Sequences and Auto-Increment

SERIAL / BIGSERIAL (Legacy)

-- Cria coluna auto-increment automaticamente + sequence
CREATE TABLE customers (
  id    SERIAL PRIMARY KEY,
  name  VARCHAR(100) NOT NULL
);
-- Equivale a criar uma SEQUENCE + DEFAULT nextval('customers_id_seq')

IDENTITY Columns (Modern — SQL Standard)

-- Preferir sobre SERIAL em novos projetos (PG 10+)
CREATE TABLE customers (
  id    INTEGER GENERATED ALWAYS AS IDENTITY PRIMARY KEY,
  name  VARCHAR(100) NOT NULL
);

-- GENERATED BY DEFAULT: permite override manual do ID
CREATE TABLE products (
  id    INTEGER GENERATED BY DEFAULT AS IDENTITY PRIMARY KEY,
  name  VARCHAR(100) NOT NULL
);

Manual Sequences

CREATE SEQUENCE seq_order_number START WITH 1000 INCREMENT BY 1;

-- Usar no INSERT
INSERT INTO orders (order_number) VALUES (nextval('seq_order_number'));

RETURNING in Delphi

///<summary>
///Insert customer and obtain the id and created_at generated by the bank.
///RETURNING works with Open (same as Firebird).
///</summary>
procedure TPostgreSQLCustomerRepository.Insert(ACustomer: TCustomer);
var
  LQuery: TFDQuery;
begin
  LQuery := TFDQuery.Create(nil);
  try
    LQuery.Connection := FConnection;
    LQuery.SQL.Text :=
      'INSERT INTO customers (name, cpf, email, status) ' +
      'VALUES (:name, :cpf, :email, :status) ' +
      'RETURNING id, created_at';
    LQuery.ParamByName('name').AsString := ACustomer.Name;
    LQuery.ParamByName('cpf').AsString := ACustomer.Cpf;
    LQuery.ParamByName('email').AsString := ACustomer.Email;
    LQuery.ParamByName('status').AsSmallInt := Ord(ACustomer.Status);

    { RETURNING: usar Open para receber o resultado }
    LQuery.Open;
    ACustomer.Id := LQuery.FieldByName('id').AsInteger;
    ACustomer.CreatedAt := LQuery.FieldByName('created_at').AsDateTime;
  finally
    LQuery.Free;
  end;
end;

UPSERT — INSERT ... ON CONFLICT

-- Inserir ou atualizar se já existir (pela constraint unique)
INSERT INTO customers (cpf, name, email, status)
VALUES (:cpf, :name, :email, :status)
ON CONFLICT (cpf) DO UPDATE SET
  name = EXCLUDED.name,
  email = EXCLUDED.email,
  status = EXCLUDED.status;

-- Ignorar se já existir (sem atualizar)
INSERT INTO customer_tags (customer_id, tag)
VALUES (:customer_id, :tag)
ON CONFLICT DO NOTHING;

In Delphi:

procedure TPostgreSQLCustomerRepository.Upsert(ACustomer: TCustomer);
var
  LQuery: TFDQuery;
begin
  LQuery := TFDQuery.Create(nil);
  try
    LQuery.Connection := FConnection;
    LQuery.SQL.Text :=
      'INSERT INTO customers (cpf, name, email, status) ' +
      'VALUES (:cpf, :name, :email, :status) ' +
      'ON CONFLICT (cpf) DO UPDATE SET ' +
      '  name = EXCLUDED.name, ' +
      '  email = EXCLUDED.email, ' +
      '  status = EXCLUDED.status ' +
      'RETURNING id';
    LQuery.ParamByName('cpf').AsString := ACustomer.Cpf;
    LQuery.ParamByName('name').AsString := ACustomer.Name;
    LQuery.ParamByName('email').AsString := ACustomer.Email;
    LQuery.ParamByName('status').AsSmallInt := Ord(ACustomer.Status);
    LQuery.Open;
    ACustomer.Id := LQuery.FieldByName('id').AsInteger;
  finally
    LQuery.Free;
  end;
end;

JSONB — Semi-Structured Data

Storage and Query

-- Tabela com coluna JSONB
CREATE TABLE customer_settings (
  customer_id  INTEGER REFERENCES customers(id),
  settings     JSONB NOT NULL DEFAULT '{}',
  PRIMARY KEY (customer_id)
);

-- Inserir JSON
INSERT INTO customer_settings (customer_id, settings)
VALUES (1, '{"theme": "dark", "language": "pt-BR", "notifications": true}');

-- Consultar campo específico
SELECT settings->>'theme' AS theme FROM customer_settings WHERE customer_id = 1;

-- Filtrar por valor JSON
SELECT * FROM customer_settings WHERE settings @> '{"theme": "dark"}';

-- Índice GIN para busca rápida em JSONB
CREATE INDEX idx_settings_gin ON customer_settings USING GIN (settings);

In Delphi:

{ Inserir JSONB }
LQuery.SQL.Text :=
  'INSERT INTO customer_settings (customer_id, settings) ' +
  'VALUES (:customer_id, :settings::jsonb)';
LQuery.ParamByName('customer_id').AsInteger := ACustomerId;
LQuery.ParamByName('settings').AsString := AJsonString;
LQuery.ExecSQL;

{ Ler campo JSONB }
LQuery.SQL.Text :=
  'SELECT settings->>''theme'' AS theme ' +
  'FROM customer_settings WHERE customer_id = :id';
LQuery.ParamByName('id').AsInteger := ACustomerId;
LQuery.Open;
LTheme := LQuery.FieldByName('theme').AsString;

Full-Text Search (FTS)

-- Coluna tsvector para busca textual
ALTER TABLE products ADD COLUMN search_vector TSVECTOR;

-- Trigger para atualizar automaticamente
CREATE OR REPLACE FUNCTION update_search_vector() RETURNS TRIGGER AS $$
BEGIN
  NEW.search_vector :=
    setweight(to_tsvector('portuguese', COALESCE(NEW.name, '')), 'A') ||
    setweight(to_tsvector('portuguese', COALESCE(NEW.description, '')), 'B');
  RETURN NEW;
END;
$$ LANGUAGE plpgsql;

CREATE TRIGGER trg_product_search BEFORE INSERT OR UPDATE
  ON products FOR EACH ROW EXECUTE FUNCTION update_search_vector();

-- Índice GIN para FTS
CREATE INDEX idx_product_search ON products USING GIN (search_vector);

-- Buscar
SELECT * FROM products
WHERE search_vector @@ plainto_tsquery('portuguese', 'camisa azul')
ORDER BY ts_rank(search_vector, plainto_tsquery('portuguese', 'camisa azul')) DESC;

In Delphi:

function TProductRepository.Search(const ASearchTerm: string): TObjectList<TProduct>;
var
  LQuery: TFDQuery;
begin
  Result := TObjectList<TProduct>.Create(True);
  LQuery := TFDQuery.Create(nil);
  try
    LQuery.Connection := FConnection;
    LQuery.SQL.Text :=
      'SELECT id, name, price, description ' +
      'FROM products ' +
      'WHERE search_vector @@ plainto_tsquery(''portuguese'', :term) ' +
      'ORDER BY ts_rank(search_vector, plainto_tsquery(''portuguese'', :term)) DESC ' +
      'LIMIT :limit';
    LQuery.ParamByName('term').AsString := ASearchTerm;
    LQuery.ParamByName('limit').AsInteger := 50;
    LQuery.Open;

    while not LQuery.Eof do
    begin
      Result.Add(MapToProduct(LQuery));
      LQuery.Next;
    end;
  finally
    LQuery.Free;
  end;
end;

CTEs (Common Table Expressions)

-- CTE para queries complexas e legíveis
WITH active_customers AS (
  SELECT id, name, email
  FROM customers
  WHERE status = 0
),
customer_orders AS (
  SELECT customer_id, COUNT(*) AS total_orders, SUM(total_amount) AS total_spent
  FROM orders
  GROUP BY customer_id
)
SELECT ac.name, ac.email, co.total_orders, co.total_spent
FROM active_customers ac
LEFT JOIN customer_orders co ON co.customer_id = ac.id
ORDER BY co.total_spent DESC NULLS LAST;

Recursive CTE

-- Hierarquia de categorias
WITH RECURSIVE category_tree AS (
  SELECT id, name, parent_id, 0 AS level
  FROM categories
  WHERE parent_id IS NULL

  UNION ALL

  SELECT c.id, c.name, c.parent_id, ct.level + 1
  FROM categories c
  JOIN category_tree ct ON c.parent_id = ct.id
)
SELECT * FROM category_tree ORDER BY level, name;

WindowFunctions

-- Ranking de clientes por valor gasto
SELECT
  c.name,
  SUM(o.total_amount) AS total_spent,
  RANK() OVER (ORDER BY SUM(o.total_amount) DESC) AS ranking,
  ROW_NUMBER() OVER (ORDER BY SUM(o.total_amount) DESC) AS row_num,
  SUM(o.total_amount) / SUM(SUM(o.total_amount)) OVER () * 100 AS percent_total
FROM customers c
JOIN orders o ON o.customer_id = c.id
GROUP BY c.id, c.name;

-- Média móvel de vendas por dia
SELECT
  order_date::DATE AS day,
  SUM(total_amount) AS daily_total,
  AVG(SUM(total_amount)) OVER (ORDER BY order_date::DATE ROWS BETWEEN 6 PRECEDING AND CURRENT ROW) AS moving_avg_7d
FROM orders
GROUP BY order_date::DATE
ORDER BY day;

Functions (PL/pgSQL)

-- Function que retorna valor (equivale a function no Delphi)
CREATE OR REPLACE FUNCTION fn_customer_full_name(p_id INTEGER)
RETURNS VARCHAR AS $$
DECLARE
  v_name VARCHAR;
BEGIN
  SELECT name INTO v_name FROM customers WHERE id = p_id;
  IF NOT FOUND THEN
    RAISE EXCEPTION 'Customer % not found', p_id;
  END IF;
  RETURN v_name;
END;
$$ LANGUAGE plpgsql;

-- Function que retorna tabela (equivale a Selectable Procedure no Firebird)
CREATE OR REPLACE FUNCTION fn_customers_by_status(p_status SMALLINT)
RETURNS TABLE (
  o_id     INTEGER,
  o_name   VARCHAR,
  o_email  VARCHAR,
  o_status SMALLINT
) AS $$
BEGIN
  RETURN QUERY
    SELECT id, name, email, status
    FROM customers
    WHERE status = p_status
    ORDER BY name;
END;
$$ LANGUAGE plpgsql;

-- Procedure (PG 11+ — sem retorno, apenas ação)
CREATE OR REPLACE PROCEDURE sp_deactivate_customer(p_id INTEGER)
LANGUAGE plpgsql AS $$
BEGIN
  UPDATE customers SET status = 1, updated_at = NOW() WHERE id = p_id;
  IF NOT FOUND THEN
    RAISE EXCEPTION 'Customer % not found', p_id;
  END IF;
END;
$$;

Call in Delphi:

{ Function escalar }
LQuery.SQL.Text := 'SELECT fn_customer_full_name(:id)';
LQuery.ParamByName('id').AsInteger := ACustomerId;
LQuery.Open;
LFullName := LQuery.Fields[0].AsString;

{ Function que retorna table (como SELECT) }
LQuery.SQL.Text := 'SELECT * FROM fn_customers_by_status(:status)';
LQuery.ParamByName('status').AsSmallInt := Ord(csActive);
LQuery.Open;

{ Procedure (PG 11+) }
LQuery.SQL.Text := 'CALL sp_deactivate_customer(:id)';
LQuery.ParamByName('id').AsInteger := ACustomerId;
LQuery.ExecSQL;

ENUM Types

-- Tipo enum nativo do PostgreSQL
CREATE TYPE order_status AS ENUM ('pending', 'processing', 'shipped', 'delivered', 'cancelled');

CREATE TABLE orders (
  id          SERIAL PRIMARY KEY,
  customer_id INTEGER NOT NULL REFERENCES customers(id),
  status      order_status NOT NULL DEFAULT 'pending',
  created_at  TIMESTAMPTZ DEFAULT NOW()
);

-- Inserir
INSERT INTO orders (customer_id, status) VALUES (1, 'processing');

In Delphi (map to Pascal enum):

type
  TOrderStatus = (osPending, osProcessing, osShipped, osDelivered, osCancelled);

const
  ORDER_STATUS_NAMES: array[TOrderStatus] of string = (
    'pending', 'processing', 'shipped', 'delivered', 'cancelled'
  );

function StringToOrderStatus(const AValue: string): TOrderStatus;
var
  LStatus: TOrderStatus;
begin
  for LStatus := Low(TOrderStatus) to High(TOrderStatus) do
    if SameText(ORDER_STATUS_NAMES[LStatus], AValue) then
      Exit(LStatus);
  raise EArgumentException.CreateFmt('Status inválido: "%s"', [AValue]);
end;

{ Ler do banco }
LOrder.Status := StringToOrderStatus(LQuery.FieldByName('status').AsString);

{ Gravar no banco }
LQuery.ParamByName('status').AsString := ORDER_STATUS_NAMES[AOrder.Status];

UUID as Primary Key

-- Usar gen_random_uuid() nativo (PG 13+)
CREATE TABLE sessions (
  id         UUID DEFAULT gen_random_uuid() PRIMARY KEY,
  user_id    INTEGER NOT NULL,
  token      VARCHAR(255),
  expires_at TIMESTAMPTZ
);

-- Para PG < 13: CREATE EXTENSION IF NOT EXISTS "uuid-ossp";
-- Então: DEFAULT uuid_generate_v4()

In Delphi:

LQuery.SQL.Text :=
  'INSERT INTO sessions (user_id, token, expires_at) ' +
  'VALUES (:user_id, :token, :expires_at) RETURNING id';
LQuery.ParamByName('user_id').AsInteger := AUserId;
LQuery.ParamByName('token').AsString := AToken;
LQuery.ParamByName('expires_at').AsDateTime := AExpiresAt;
LQuery.Open;
LSessionId := LQuery.FieldByName('id').AsString; { UUID como string }

Transactions and Isolation Levels

Isolation Levels in PostgreSQL

Explicit Transaction

procedure ExecuteInTransaction(AConnection: TFDConnection; AProc: TProc);
begin
  AConnection.StartTransaction;
  try
    AProc;
    AConnection.Commit;
  except
    AConnection.Rollback;
    raise;
  end;
end;

SAVEPOINT (Partial Transaction)

{ PostgreSQL suporta SAVEPOINT para rollback parcial }
FConnection.StartTransaction;
try
  FCustomerRepo.Insert(LCustomer);

  FConnection.ExecSQL('SAVEPOINT before_order');
  try
    FOrderRepo.Insert(LOrder);
  except
    FConnection.ExecSQL('ROLLBACK TO SAVEPOINT before_order');
    { Customer foi salvo, order não }
  end;

  FConnection.Commit;
except
  FConnection.Rollback;
  raise;
end;

LISTEN / NOTIFY (Bank Events)

-- No PostgreSQL: notificações assíncronas
-- Em uma trigger:
CREATE OR REPLACE FUNCTION notify_new_order() RETURNS TRIGGER AS $$
BEGIN
  PERFORM pg_notify('new_order', json_build_object('id', NEW.id, 'customer_id', NEW.customer_id)::TEXT);
  RETURN NEW;
END;
$$ LANGUAGE plpgsql;

CREATE TRIGGER trg_order_notify AFTER INSERT ON orders
  FOR EACH ROW EXECUTE FUNCTION notify_new_order();

{ No Delphi: escutar eventos via FireDAC Event Alerter }
uses
  FireDAC.Phys.PG;

var
  LAlerter: TFDEventAlerter;
begin
  LAlerter := TFDEventAlerter.Create(nil);
  try
    LAlerter.Connection := FConnection;
    LAlerter.DriverName := 'PG';
    LAlerter.Names.Text := 'new_order';
    LAlerter.Options.Timeout := 0;
    LAlerter.OnAlert := HandleNewOrderEvent;
    LAlerter.Active := True;
  finally
    { Manter vivo enquanto a aplicação rodar }
  end;
end;

procedure TMyService.HandleNewOrderEvent(ASender: TFDCustomEventAlerter;
  const AEventName: string; const AArgument: Variant);
begin
  { AArgument contém o payload JSON enviado pelo pg_notify }
  if AEventName = 'new_order' then
    ProcessNewOrderNotification(VarToStr(AArgument));
end;

Schemas

-- Schemas para organizar objetos do banco
CREATE SCHEMA IF NOT EXISTS app;
CREATE SCHEMA IF NOT EXISTS audit;

-- Tabelas em schemas diferentes
CREATE TABLE app.customers (...);
CREATE TABLE audit.log (...);

-- Search path: define schemas visíveis por padrão
SET search_path TO app, public;

In Delphi:

{ Definir schema padrão na conexão }
FConnection.Params.Values['MetaDefSchema'] := 'app';

{ Ou via SQL }
FConnection.ExecSQL('SET search_path TO app, public');

Partitioning (PG 10+)

-- Particionamento por intervalo de data
CREATE TABLE orders (
  id          SERIAL,
  customer_id INTEGER NOT NULL,
  order_date  DATE NOT NULL,
  total       NUMERIC(15,2),
  status      SMALLINT DEFAULT 0
) PARTITION BY RANGE (order_date);

-- Partições por ano
CREATE TABLE orders_2024 PARTITION OF orders
  FOR VALUES FROM ('2024-01-01') TO ('2025-01-01');
CREATE TABLE orders_2025 PARTITION OF orders
  FOR VALUES FROM ('2025-01-01') TO ('2026-01-01');
CREATE TABLE orders_2026 PARTITION OF orders
  FOR VALUES FROM ('2026-01-01') TO ('2027-01-01');

-- Índice na tabela particionada (criado em todas as partições)
CREATE INDEX idx_orders_customer ON orders (customer_id);

Schema Creation — Migration Script

/* migration_001_initial_schema.sql */

/* ===== Extensions ===== */
CREATE EXTENSION IF NOT EXISTS "uuid-ossp";
CREATE EXTENSION IF NOT EXISTS "pgcrypto";

/* ===== ENUM Types ===== */
CREATE TYPE customer_status AS ENUM ('active', 'inactive', 'suspended');
CREATE TYPE order_status AS ENUM ('pending', 'processing', 'shipped', 'delivered', 'cancelled');

/* ===== Tables ===== */
CREATE TABLE IF NOT EXISTS customers (
  id         INTEGER GENERATED ALWAYS AS IDENTITY PRIMARY KEY,
  name       VARCHAR(100) NOT NULL,
  cpf        VARCHAR(14) UNIQUE,
  email      VARCHAR(150),
  status     customer_status NOT NULL DEFAULT 'active',
  notes      TEXT,
  metadata   JSONB DEFAULT '{}',
  created_at TIMESTAMPTZ DEFAULT NOW(),
  updated_at TIMESTAMPTZ DEFAULT NOW()
);

CREATE TABLE IF NOT EXISTS products (
  id          INTEGER GENERATED ALWAYS AS IDENTITY PRIMARY KEY,
  name        VARCHAR(100) NOT NULL,
  price       NUMERIC(15, 2) NOT NULL DEFAULT 0,
  stock_qty   INTEGER NOT NULL DEFAULT 0 CHECK (stock_qty >= 0),
  description TEXT,
  tags        TEXT[] DEFAULT '{}',
  status      customer_status NOT NULL DEFAULT 'active',
  search_vector TSVECTOR,
  created_at  TIMESTAMPTZ DEFAULT NOW()
);

CREATE TABLE IF NOT EXISTS orders (
  id            INTEGER GENERATED ALWAYS AS IDENTITY PRIMARY KEY,
  customer_id   INTEGER NOT NULL REFERENCES customers(id) ON DELETE RESTRICT,
  order_date    TIMESTAMPTZ DEFAULT NOW() NOT NULL,
  total_amount  NUMERIC(15, 2) NOT NULL DEFAULT 0,
  status        order_status NOT NULL DEFAULT 'pending',
  created_at    TIMESTAMPTZ DEFAULT NOW()
);

CREATE TABLE IF NOT EXISTS order_items (
  id          INTEGER GENERATED ALWAYS AS IDENTITY PRIMARY KEY,
  order_id    INTEGER NOT NULL REFERENCES orders(id) ON DELETE CASCADE,
  product_id  INTEGER NOT NULL REFERENCES products(id) ON DELETE RESTRICT,
  quantity    INTEGER NOT NULL CHECK (quantity > 0),
  unit_price  NUMERIC(15, 2) NOT NULL,
  total_price NUMERIC(15, 2) GENERATED ALWAYS AS (quantity * unit_price) STORED
);

/* ===== Indices ===== */
CREATE INDEX idx_customer_name     ON customers (name);
CREATE INDEX idx_customer_cpf      ON customers (cpf);
CREATE INDEX idx_order_date        ON orders (order_date);
CREATE INDEX idx_order_customer    ON orders (customer_id);
CREATE INDEX idx_item_order        ON order_items (order_id);
CREATE INDEX idx_product_search    ON products USING GIN (search_vector);

/* ===== Functions ===== */
CREATE OR REPLACE FUNCTION update_updated_at_column()
RETURNS TRIGGER AS $$
BEGIN
  NEW.updated_at = NOW();
  RETURN NEW;
END;
$$ LANGUAGE plpgsql;

CREATE TRIGGER trg_customer_updated BEFORE UPDATE ON customers
  FOR EACH ROW EXECUTE FUNCTION update_updated_at_column();

Schema migration in Delphi

///<summary>
///Checks whether a table exists in PostgreSQL.
///</summary>
function TableExists(AConnection: TFDConnection; const ATableName: string;
  const ASchema: string = 'public'): Boolean;
var
  LQuery: TFDQuery;
begin
  LQuery := TFDQuery.Create(nil);
  try
    LQuery.Connection := AConnection;
    LQuery.SQL.Text :=
      'SELECT COUNT(*) FROM information_schema.tables ' +
      'WHERE table_schema = :schema AND table_name = :name';
    LQuery.ParamByName('schema').AsString := ASchema;
    LQuery.ParamByName('name').AsString := ATableName.ToLower;
    LQuery.Open;
    Result := LQuery.Fields[0].AsInteger > 0;
  finally
    LQuery.Free;
  end;
end;

///<summary>
///Checks whether a column exists in a table.
///</summary>
function ColumnExists(AConnection: TFDConnection;
  const ATableName, AColumnName: string;
  const ASchema: string = 'public'): Boolean;
var
  LQuery: TFDQuery;
begin
  LQuery := TFDQuery.Create(nil);
  try
    LQuery.Connection := AConnection;
    LQuery.SQL.Text :=
      'SELECT COUNT(*) FROM information_schema.columns ' +
      'WHERE table_schema = :schema AND table_name = :table AND column_name = :col';
    LQuery.ParamByName('schema').AsString := ASchema;
    LQuery.ParamByName('table').AsString := ATableName.ToLower;
    LQuery.ParamByName('col').AsString := AColumnName.ToLower;
    LQuery.Open;
    Result := LQuery.Fields[0].AsInteger > 0;
  finally
    LQuery.Free;
  end;
end;

PostgreSQL Error Handling

except
  on E: EFDDBEngineException do
  begin
    case E.Kind of
      ekUKViolated:
        raise EDuplicateException.Create('Registro duplicado: ' + E.Message);
      ekFKViolated:
        raise EDependencyException.Create('Violação de FK: ' + E.Message);
      ekRecordLocked:
        raise EConflictException.Create('Registro bloqueado por outra transação');
      ekServerGone:
        raise EConnectionLostException.Create('Conexão com PostgreSQL perdida');
    else
      raise;
    end;
  end;
end;

{ Verificar código de erro PostgreSQL específico }
except
  on E: EFDDBEngineException do
  begin
    { Códigos SQLSTATE do PostgreSQL: }
    { 23505 = unique_violation }
    { 23503 = foreign_key_violation }
    { 23502 = not_null_violation }
    { 40001 = serialization_failure }
    { 40P01 = deadlock_detected }
    if E.Errors[0].ErrorCode = 23505 then
      raise EDuplicateException.Create('Valor duplicado')
    else
      raise;
  end;
end;

Useful Extensions

-- pgcrypto: criptografia
CREATE EXTENSION IF NOT EXISTS pgcrypto;
SELECT crypt('senha123', gen_salt('bf'));  -- bcrypt hash

-- pg_trgm: busca por similaridade (LIKE otimizado)
CREATE EXTENSION IF NOT EXISTS pg_trgm;
CREATE INDEX idx_customer_name_trgm ON customers USING GIN (name gin_trgm_ops);
SELECT * FROM customers WHERE name % 'Joao';  -- busca fuzzy

-- uuid-ossp: geração de UUID (PG < 13, se gen_random_uuid não disponível)
CREATE EXTENSION IF NOT EXISTS "uuid-ossp";

PostgreSQL Anti-Patterns to Avoid

//❌ Concatenar SQL — SQL Injection
LQuery.SQL.Text := 'SELECT * FROM customers WHERE name = ''' + AName + '''';

//✅ Parameterized parameters
LQuery.SQL.Text := 'SELECT * FROM customers WHERE name = :name';
LQuery.ParamByName('name').AsString := AName;

//❌ ExecSQL with RETURNING — loses the result
LQuery.SQL.Text := 'INSERT INTO ... RETURNING id';
LQuery.ExecSQL;

//✅ Open com RETURNING
LQuery.SQL.Text := 'INSERT INTO ... RETURNING id';
LQuery.Open;

//❌ SELECT * on large tables
LQuery.SQL.Text := 'SELECT * FROM orders';

//✅ Select only necessary columns + LIMIT
LQuery.SQL.Text := 'SELECT id, customer_id, total FROM orders LIMIT :limit';

//❌ N+1 queries (loop with query inside)
for I := 0 to LCustomers.Count - 1 do
begin
  LQuery.SQL.Text := 'SELECT COUNT(*) FROM orders WHERE customer_id = :id';
  // ...
end;

//✅ JOIN ou subquery
LQuery.SQL.Text :=
  'SELECT c.*, (SELECT COUNT(*) FROM orders o WHERE o.customer_id = c.id) AS order_count ' +
  'FROM customers c';

//❌ Use SERIAL when IDENTITY is better
CREATE TABLE t (id SERIAL PRIMARY KEY);

//✅ Usar IDENTITY (SQL Standard)
CREATE TABLE t (id INTEGER GENERATED ALWAYS AS IDENTITY PRIMARY KEY);

//❌ Ignore indexes on filtered columns
SELECT * FROM orders WHERE customer_id = 1;  -- sem índice = full scan

//✅ Create indexes for columns used in WHERE, JOIN, ORDER BY
CREATE INDEX idx_order_customer ON orders (customer_id);

Key Differences: PostgreSQL vs Firebird

PostgreSQL Checklist

• Driver PG configured?
• Connection string with Server, Port, Database, UserName, Password?
• CharacterSet := 'UTF8' defined?
• Parameterized queries (without string concatenation)?
• RETURNING with Open (not ExecSQL)?
• IDENTITY instead of SERIAL for new projects?
• Explicit transactions for compound operations?
• Errors handled via EFDDBEngineException.Kind?
• libpq.dll (32/64-bit) in PATH or configured in VendorLib?
• Indexes created for columns used in WHERE and JOIN?
• Foreign Keys with appropriate ON DELETE/ON UPDATE?
• JSONB for semi-structured data (instead of TEXT)?
• information_schema to check metadata (not RDB$)?