Function alterTableColumn

packages/sql/src/schema/SchemaHelper.ts:680–733

(column: Column, table: DatabaseTable, changedProperties: Set<string>)

  }

  alterTableColumn(column: Column, table: DatabaseTable, changedProperties: Set<string>): string[] {
    const sql: string[] = [];
    const typeChanged = changedProperties.has('type') || changedProperties.has('collation');
    const defaultChanged = changedProperties.has('default');
    // Postgres can't implicitly cast a stored DEFAULT across array element types
    // (e.g. `'{}'::text[]` -> `numeric(3,2)[]`), so drop+re-set it around ALTER TYPE.
    const fromColumn = typeChanged ? table.getColumn(column.name) : undefined;
    const needsArrayDefaultRecast =
      typeChanged &&
      fromColumn?.default != null &&
      fromColumn.type.endsWith(']') &&
      column.type.endsWith(']') &&
      fromColumn.type !== column.type;
    const recastDefault = needsArrayDefaultRecast && !defaultChanged;

    if ((defaultChanged && column.default == null) || needsArrayDefaultRecast) {
      sql.push(`alter table ${table.getQuotedName()} alter column ${this.quote(column.name)} drop default`);
    }

    if (typeChanged) {
      let type = column.type + (column.generated ? ` generated always as ${column.generated}` : '');

      if (column.nativeEnumName) {
        const parts = type.split('.');

        if (parts.length === 2 && parts[0] === '*' && table.schema) {
          type = `${table.schema}.${parts[1]}`;
        } else if (parts.length === 1) {
          type = this.getTableName(type, table.schema);
        }

        type = this.quote(type);
      }

      const collateClause = column.collation ? ` ${this.getCollateSQL(column.collation)}` : '';

      sql.push(
        `alter table ${table.getQuotedName()} alter column ${this.quote(column.name)} type ${type + collateClause + this.castColumn(column.name, type)}`,
      );
    }

    if ((defaultChanged && column.default != null) || recastDefault) {
      sql.push(
        `alter table ${table.getQuotedName()} alter column ${this.quote(column.name)} set default ${column.default}`,
      );
    }

    if (changedProperties.has('nullable')) {
      const action = column.nullable ? 'drop' : 'set';
      sql.push(`alter table ${table.getQuotedName()} alter column ${this.quote(column.name)} ${action} not null`);
    }

    return sql;
  }

  /** Returns the bare `collate <name>` clause for column DDL. Overridden by PostgreSQL to quote the identifier. */
  protected getCollateSQL(collation: string): string {