一：IF-THEN语句

IF (condition) THEN    commands;END IF;

 

二：IF-THEN_ELSE语句

IF (condition) THEN   S1; ELSE    S2;END IF;

 

三：IF-THEN—ELSEIF—ELSE

IF(boolean_expression 1)THEN    S1; ELSIF( boolean_expression 2) THEN   S2; ELSIF( boolean_expression 3) THEN   S3;ELSE    S4;END IF;

 

四：CASE语句

CASE selector    WHEN 'value1' THEN S1;    WHEN 'value2' THEN S2;    WHEN 'value3' THEN S3;    ...    ELSE Sn;  -- default caseEND CASE;

CASE    WHEN selector = 'value1' THEN S1;    WHEN selector = 'value2' THEN S2;    WHEN selector = 'value3' THEN S3;    ...    ELSE Sn;  -- default caseEND CASE;