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How to map keys to values for an individual field in a MySQL select query?
You can use CASE statement in MySQL to map keys to values for an individual field in select query. The syntax is as follows −
SELECT yourColumnName1,yourColumnName2,yourColumnName3,.........N ( CASE WHEN yourColumnName = 1 THEN 'ENABLED' ELSE 'DISABLED' END ) AS anyVariableName FROM yourTableName;
You can use IF() function also for the same purpose. The syntax is as follows −
SELECT yourColumnName1,yourColumnName2,yourColumnName3,.........N ,IF(yourColumnName,'ENABLED','DISABLED') as anyVariableName FROM yourTableName;
To understand the above syntax, let us create a table. The query to create a table is as follows −
mysql> create table MapKeys -> ( -> Id int NOT NULL AUTO_INCREMENT, -> Name varchar(20), -> isActive boolean, -> PRIMARY KEY(Id) -> ); Query OK, 0 rows affected (0.65 sec)
Insert some records in the table using insert command. The query is as follows −
mysql> insert into MapKeys(Name,isActive) values('Larry',true);
Query OK, 1 row affected (0.13 sec)
mysql> insert into MapKeys(Name,isActive) values('David',false);
Query OK, 1 row affected (0.16 sec)
mysql> insert into MapKeys(Name,isActive) values('Mike',true);
Query OK, 1 row affected (0.14 sec)
mysql> insert into MapKeys(Name,isActive) values('Carol',false);
Query OK, 1 row affected (0.17 sec)
mysql> insert into MapKeys(Name,isActive) values('Sam',false);
Query OK, 1 row affected (0.15 sec)
mysql> insert into MapKeys(Name,isActive) values('Bob',true);
Query OK, 1 row affected (0.19 sec)Display all records from the table using select statement. The query is as follows:
mysql> select *from MapKeys;
The following is the output −
+----+-------+----------+ | Id | Name | isActive | +----+-------+----------+ | 1 | Larry | 1 | | 2 | David | 0 | | 3 | Mike | 1 | | 4 | Carol | 0 | | 5 | Sam | 0 | | 6 | Bob | 1 | +----+-------+----------+ 6 rows in set (0.00 sec)
Let us now map key using case statement. The query is as follows −
mysql> select Id,Name, -> ( -> CASE WHEN isActive = 1 THEN 'ENABLED' -> ELSE 'DISABLED' -> END -> ) AS Status -> from MapKeys;
The following is the output −
+----+-------+----------+ | Id | Name | Status | +----+-------+----------+ | 1 | Larry | ENABLED | | 2 | David | DISABLED | | 3 | Mike | ENABLED | | 4 | Carol | DISABLED | | 5 | Sam | DISABLED | | 6 | Bob | ENABLED | +----+-------+----------+ 6 rows in set (0.00 sec)
You can achieve the same with the help of IF() function −
mysql> select Id,Name,if(isActive,'ENABLED','DISABLED') as Status from MapKeys;
The following is the output −
+----+-------+----------+ | Id | Name | Status | +----+-------+----------+ | 1 | Larry | ENABLED | | 2 | David | DISABLED | | 3 | Mike | ENABLED | | 4 | Carol | DISABLED | | 5 | Sam | DISABLED | | 6 | Bob | ENABLED | +----+-------+----------+ 6 rows in set (0.00 sec)
Updated on: 30-Jun-2020
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