MySQL Using Variables Row Number and Group By using variables in Select Statement
Example
Let's say we have a table team_person as below:
+======+===========+
| team | person |
+======+===========+
| A | John |
+------+-----------+
| B | Smith |
+------+-----------+
| A | Walter |
+------+-----------+
| A | Louis |
+------+-----------+
| C | Elizabeth |
+------+-----------+
| B | Wayne |
+------+-----------+
CREATE TABLE team_person AS SELECT 'A' team, 'John' person
UNION ALL SELECT 'B' team, 'Smith' person
UNION ALL SELECT 'A' team, 'Walter' person
UNION ALL SELECT 'A' team, 'Louis' person
UNION ALL SELECT 'C' team, 'Elizabeth' person
UNION ALL SELECT 'B' team, 'Wayne' person;
To select the table team_person with additional row_number column, either
SELECT @row_no := @row_no+1 AS row_number, team, person
FROM team_person, (SELECT @row_no := 0) t;
OR
SET @row_no := 0;
SELECT @row_no := @row_no + 1 AS row_number, team, person
FROM team_person;
will output the result below:
+============+======+===========+
| row_number | team | person |
+============+======+===========+
| 1 | A | John |
+------------+------+-----------+
| 2 | B | Smith |
+------------+------+-----------+
| 3 | A | Walter |
+------------+------+-----------+
| 4 | A | Louis |
+------------+------+-----------+
| 5 | C | Elizabeth |
+------------+------+-----------+
| 6 | B | Wayne |
+------------+------+-----------+
Finally, if we want to get the row_number group by column team
SELECT @row_no := IF(@prev_val = t.team, @row_no + 1, 1) AS row_number
,@prev_val := t.team AS team
,t.person
FROM team_person t,
(SELECT @row_no := 0) x,
(SELECT @prev_val := '') y
ORDER BY t.team ASC,t.person DESC;
+============+======+===========+
| row_number | team | person |
+============+======+===========+
| 1 | A | Walter |
+------------+------+-----------+
| 2 | A | Louis |
+------------+------+-----------+
| 3 | A | John |
+------------+------+-----------+
| 1 | B | Wayne |
+------------+------+-----------+
| 2 | B | Smith |
+------------+------+-----------+
| 1 | C | Elizabeth |
+------------+------+-----------+
