How do I lag columns in MySQL?

MySQLMySQLi Database

To lag a column in MySQL, first, let us create a table. The query to create a table is as follows −

mysql> create table LagDemo
   -> (
   -> UserId int,
   -> UserValue int
   -> );
Query OK, 0 rows affected (1.74 sec)

Example

Insert some records in the table using insert command. The query is as follows −

mysql> insert into LagDemo values(12,158);
Query OK, 1 row affected (0.61 sec)
mysql> insert into LagDemo values(18,756);
Query OK, 1 row affected (0.21 sec)
mysql> insert into LagDemo values(15,346);
Query OK, 1 row affected (0.25 sec)
mysql> insert into LagDemo values(87,646);
Query OK, 1 row affected (0.14 sec)
mysql> insert into LagDemo values(27,334);
Query OK, 1 row affected (0.11 sec)
mysql> insert into LagDemo values(90,968);
Query OK, 1 row affected (0.08 sec)
mysql> insert into LagDemo values(84,378);
Query OK, 1 row affected (0.10 sec)
mysql> insert into LagDemo values(85,546);
Query OK, 1 row affected (0.56 sec)

Display all records from the table using a select statement. The query is as follows −

mysql> select *from LagDemo;

Output

+--------+-----------+
| UserId | UserValue |
+--------+-----------+
|     12 |       158 |
|     18 |       756 |
|     15 |       346 |
|     87 |       646 |
|     27 |       334 |
|     90 |       968 |
|     84 |       378 |
|     85 |       546 |
+--------+-----------+
8 rows in set (0.00 sec)

Here is the query to lag a column in MySQL −

mysql> SET @f : = 0;
Query OK, 0 rows affected (0.00 sec)
mysql> SET @s : = 2;
Query OK, 0 rows affected (0.00 sec)
mysql> SELECT l1.UserId, l1.UserValue , l1.UserValue / l2.UserValue AS 'LAG'
-> FROM
-> (SELECT if(@f, @f: = @f+1, @f:=1) as RowNumber, UserId, UserValue FROM LagDemo) AS l1
-> LEFT JOIN
-> (SELECT if(@s, @s: = @s+1, @s: = 1) as RowNumber, UserId, UserValue FROM LagDemo) AS l2
-> ON l1.RowNumber = l2.RowNumber;

Output

+--------+-----------+--------+
| UserId | UserValue |    LAG |
+--------+-----------+--------+
|     12 |       158 |   NULL |
|     18 |       756 |   NULL |
|     15 |       346 | 2.1899 |
|     87 |       646 | 0.8545 |
|     27 |       334 | 0.9653 |
|     90 |       968 | 1.4985 |
|     84 |       378 | 1.1317 |
|     85 |       546 | 0.5640 |
+--------+-----------+--------+
8 rows in set (0.00 sec)
raja
Published on 19-Mar-2019 07:22:49
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