How to conditionally select certain fields in MySQL statement

Ask Time：2016-07-04T18:50:10 Author：Chris

I have a SELECT statement which takes various fields from different tables in my database using LEFT JOIN. I'd like to select additional fields only when a certain condition is met. Here's an example of what I'm trying to achieve.

SELECT table1.useriD, 
       table1.name, 
       table2.address, 
       table2.employed 
       (IF table2.employed = 1, 
        SELECT table3.jobTitle)
FROM table1 
LEFT JOIN table2 ON table1.userID = table2.userID
LEFT JOIN table3 ON table2.userID = table3.userID

Just to clarify, the above example is completely made up, but it demonstrates what I'm trying to do. I know that the 'IF' statement in the middle is completely wrong - this is the bit I need help with. I've looked at MySQL IF statements and the MySQL IF function but can't figure out how it should work.

Any help much appreciated.

Thanks!

Author:Chris，eproduced under the CC 4.0 BY-SA copyright license with a link to the original source and this disclaimer.
Link to original article：https://stackoverflow.com/questions/38182885/how-to-conditionally-select-certain-fields-in-mysql-statement

Blank :

IF clause likes this;)\n\nSELECT table1.useriD, \n table1.name, \n table2.address, \n table2.employed, \n IF(table2.employed = 1, table3.jobTitle, null) AS additionalCol\nFROM table1 \nLEFT JOIN table2 ON table1.userID = table2.userID\nLEFT JOIN table3 ON table2.userID = table3.userID\n\n\nAlso you can use CASE WHEN:\n\nSELECT table1.useriD, \n table1.name, \n table2.address, \n table2.employed, \n CASE WHEN table2.employed = 1 THEN table3.jobTitle ELSE null END AS additionalCol\nFROM table1 \nLEFT JOIN table2 ON table1.userID = table2.userID\nLEFT JOIN table3 ON table2.userID = table3.userID\n",

2016-07-04T10:53:52

currarpickt :

SELECT table1.useriD, \n table1.name, \n table2.address, \n table2.employed, \n (IF table2.employed = 1, table3.jobTitle, null) as JobTitle\nFROM table1 \nLEFT JOIN table2 ON table1.userID = table2.userID\nLEFT JOIN table3 ON table2.userID = table3.userID\n\n\nReference: http://dev.mysql.com/doc/refman/5.7/en/control-flow-functions.html",

2016-07-04T10:54:07

How to conditionally select certain fields in MySQL statement