Requirements: according to whether a table is empty, decided to perform different SQL statements
Whether can use SQL to achieve without stored procedure directly?

CodePudding user response:

My train of thought is directly using if.. The else..

 BEGIN 
IF (SELECT count (*) FROM t1)=0 
THEN SELECT count (*) FROM t1; 
The ELSE SELECT count (*) FROM t2; 
END the IF; 
END; 

Perform error, IF grammar mistakes, to solve

CodePudding user response:

 
SELECT the IIF (COUNT (*)=0, (SELECT COUNT (*) FROM t1), (SELECT COUNT (*) FROM t2)) FROM t1 

 
The SELECT (CASE WHEN the COUNT (*)=0 THEN COUNT (*) ELSE (SELECT COUNT (*) FROM t2) END) COUNT FROM t1 

CodePudding user response:

 



Declare @ a int 
The set @ a=1 

If @ a=1 
The begin 
Select the 'a' 
End 


If @ a=2 
The begin 
Select 'b' 
End 

Is that ok?

CodePudding user response:

Thinking no problem of the building Lord, is the problem writing some

 IF 
(
SELECT COUNT (*) FROM t1 
)=0 
The BEGIN 
SELECT COUNT (*) 
The FROM t1; 
END; 

The ELSE 
The BEGIN 
SELECT COUNT (*) 
The FROM t2. 
END; 

CodePudding user response:

reference floor 6 February 16 response:

thinking no problem of the building Lord, is the problem writing some

 IF 
(
SELECT COUNT (*) FROM t1 
)=0 
The BEGIN 
SELECT COUNT (*) 
The FROM t1; 
END; 

The ELSE 
The BEGIN 
SELECT COUNT (*) 
The FROM t2. 
END; 

Write grammatical errors, I used the PGSQL

CodePudding user response:

Help you move to the pg SQL section,

CodePudding user response:

You need to use function (stored procedure), not a single statement