jak upuścić kolumnę, jeśli istnieje w mysql?

Question

ALTER TABLE user DROP COLUMN registered_date 

Możemy upuścić kolumnę za pomocą powyższego polecenia. Ale jak mogę go upuścić tylko wtedy, gdy istnieje kolumna registered_date?

Answer 1

IF EXISTS(SELECT * 
      FROM information_schema.COLUMNS 
      WHERE 
      TABLE_SCHEMA = 'db_name' 
      AND TABLE_NAME = 'table_name' 
      AND COLUMN_NAME = 'column_name') 
BEGIN 
ALTER TABLE table_name DROP COLUMN column_name 
END 

LUB

IF (SELECT COUNT(*) 
      FROM information_schema.COLUMNS 
      WHERE 
      TABLE_SCHEMA = 'db_name' 
      AND TABLE_NAME = 'table_name' 
      AND COLUMN_NAME = 'column_name'>0) 
BEGIN 
ALTER TABLE table_name DROP COLUMN column_name 
END