CODEWITHSUNDEEP
mysql
axon
axon

Reputation: 109

How to check if rows were returned in a SELECT statement and run another query based on that

Is it possible to check the result of a SELECT statement, and based on whether rows were returned from that query or not, execute another SELECT statement?

I had the following in mind, but it doesn't work.

SELECT IF(
  (SELECT * FROM client_emails ce WHERE ce.client_id = 3),
    (SELECT * FROM client_emails ce WHERE ce.client_id = 3),
    (SELECT * FROM emails)
)

Upvotes: 0

Views: 290

Answers (1)

dfdsfdsfsdf
dfdsfdsfsdf

Reputation: 663

you can definitely check for nulls.

Here's a sample code that'll show you how to check for nulls and use it in a conditional block using TSQL

--check for null
SELECT *
FROM dbo.Accounts
WHERE name IS NOT NULL

--check for non-null 
SELECT *
FROM dbo.Accounts
WHERE name IS NOT NULL


--checking for null in conditional block
IF(EXISTS(SELECT 1 FROM dbo.Accounts WHERE name IS NULL))
BEGIN
    --create new account
    INSERT INTO dbo.Account
    VALUES('John')
END

----------------- UPDATE TO YOUR COMMMENT ------------------------

based on the 1st code sample, you know that you can check if a row exist or not by using EXISTS. so, if you spent some time thinking about it, you would realize that you can do something like the following

/*

    Execute SELECT statement A.
        If rows had been returned,
            Execute SELECT statement B.
*/
--statement B
SELECT *
FROM dbo.Accounts a
WHERE a.name = 'John' 
AND EXISTS
(
    --statement A
        SELECT 1 
        FROM dbo.Address 
        WHERE account_id = a.account_id 
)

/*

If rows had not been returned,
    Execute SELECT statement C.
*/
--statement c
SELECT *
FROM dbo.Accounts a
WHERE a.name = 'David' 
AND NOT EXISTS
(
    --statement A
        SELECT 1 
        FROM dbo.Address 
        WHERE account_id = a.account_id 
)

Upvotes: 1

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