Add limited support for PostgreSql CREATE TRIGGER and CREATE FUNCTION

[griffio]

Fixes #4812 #4795

PostgreSql Experimental 🍄😵

Very limited support for CREATE TRIGGER and CREATE FUNCTION used together - not for stand-alone CREATE FUNCTION use. DROP TRIGGER and DROP FUNCTION are also supported.

PostgreSql uses functions to execute the trigger DML unlike Sqlite where the trigger contains the executed statements.

Various fixes had to be made to override the Sqlite CREATE TRIGGER - e.g Fixtures tests that are invalid PostgreSql statements. Currently avoids the need to change sql-psi by reusing existing public core classes.

Supported Features

Call multiple statements Delete, Insert, Update e.g Insert a row into an audit table when a column is updated.

Using new and old table row references are case-sensitive because SqlDelight is when referencing table names.

CREATE TABLE accounts(
  id INT GENERATED ALWAYS AS IDENTITY,
  balance REAL
);

CREATE TABLE accounts_audit (
   account_id INT,
   balance REAL,
   changed_on TIMESTAMP NOT NULL
);

CREATE OR REPLACE TRIGGER check_update
    BEFORE UPDATE OF balance ON accounts
    FOR EACH ROW
    EXECUTE FUNCTION account_audit_update();

CREATE OR REPLACE FUNCTION account_audit_update()
RETURNS TRIGGER LANGUAGE PLPGSQL AS
$$
BEGIN
    INSERT INTO accounts_audit(account_id, balance, changed_on) VALUES (old.id, old.balance, NOW());
    RETURN new;
END;
$$;

Assign values to new records e.g Assign the current timestamp to a column each time a row is updated.
Multiple statements e.g other assignments and deletes, inserts and updates can be mixed.

CREATE TABLE organizations (
  id INTEGER NOT NULL,
  name TEXT NOT NULL,
  updated_at TIMESTAMP DEFAULT NOW() NOT NULL
);

CREATE TRIGGER organizations_set_updated_at
BEFORE UPDATE ON organizations
FOR EACH ROW
EXECUTE FUNCTION organizations_set_updated_at();

CREATE OR REPLACE FUNCTION organizations_set_updated_at()
RETURNS TRIGGER LANGUAGE PLPGSQL AS
$$
BEGIN
  new.updated_at := NOW(); 
  RETURN new;
END;
$$;

Conditionals IF ELSEIF ELSE

CREATE TABLE user_profile (
  username TEXT NOT NULL UNIQUE,
  password TEXT NOT NULL,
  password_strength TEXT
);

CREATE OR REPLACE FUNCTION user_profile_password_strength()
RETURNS TRIGGER LANGUAGE PLPGSQL AS $$
BEGIN

  IF TG_OP = 'UPDATE' AND new.password IS NOT DISTINCT FROM old.password THEN
    RETURN new;
  END IF;

  IF length(new.password) < 6 THEN
    new.password_strength := 'weak';
  ELSIF length(new.password) < 12 THEN
    new.password_strength := 'medium';
  ELSE
    new.password_strength := 'strong';
  END IF;

  RETURN new;
END;
$$;

CREATE TRIGGER user_profile_password_strength
BEFORE INSERT OR UPDATE OF password
ON user_profile
FOR EACH ROW
EXECUTE FUNCTION user_profile_password_strength();

Add Trigger variables

CREATE OR REPLACE FUNCTION process_emp_audit()
RETURNS TRIGGER LANGUAGE PLPGSQL AS $$
BEGIN
    IF (TG_OP = 'DELETE') THEN
        INSERT INTO emp_audit SELECT 'D', NOW(), CURRENT_USER, old.empname, old.salary;
    ELSIF (TG_OP = 'UPDATE') THEN
        INSERT INTO emp_audit SELECT 'U', NOW(), CURRENT_USER, new.empname, new.salary;
    ELSIF (TG_OP = 'INSERT') THEN
        INSERT INTO emp_audit SELECT 'I', NOW(), CURRENT_USER, new.empname, new.salary;
    END IF;
    RETURN NULL; 
END;
$$;

DROP TRIGGER IF EXISTS organizations_set_updated_at ON organisations CASCADE;

DROP FUNCTION IF EXISTS organizations_set_updated_at() CASCADE;

Adds Extension statements (e.g CREATE FUNCTION) that implement SchemaContributor - to DataBaseGenerator isSchema check - so these are included in the body of the generated Schema Sample.Schema.create(driver). As the isSchema uses hard coded list of known statement types another way is needed to include a dialects schema statements e.g function, sequence.

Adds Migration Integration Test

Notes:

• Future changes to improve support for plpgsql https://www.postgresql.org/docs/current/plpgsql-trigger.html
• The notifyQueries emit is not supported for tables in trigger function (notify is not implemented for PostgreSql anyway).

---

• CHANGELOG.md's "Unreleased" section has been updated, if applicable.

[JakeWharton]

I do not feel qualified to review this. Looks mostly fine, though.