MySQL: Insert records virtually in SELECT statement - mysql

Question

I get a set of result as follows
C1 C2 C3
10 2 T
10 3 E
10 6 S
I want my SELECT query in such a way that resultant records may look like
C1 C2 C3
10 2 T
10 3 E
10 4
10 5
10 6 S
where there is a blank line for the missing records. Couldn't figure out the same.
Original query: select C1, C2,C3 from Table

Answer 1

If your mysql version upper than 8.0, you can try to use cte RECURSIVE make a calendar table then do outer join
Schema (MySQL v8.0)
CREATE TABLE T(
C1 int,
C2 int,
C3 varchar(5)
);
INSERT INTO T VALUES (10,2,'T');
INSERT INTO T VALUES (10,3,'E');
INSERT INTO T VALUES (10,6,'S');
Query #1
WITH RECURSIVE CTE AS (
SELECT C1,MIN(C2) minC2,MAX(C2) maxC2
FROM T
GROUP BY C1
UNION ALL
SELECT C1,minC2 +1,maxC2
FROM CTE
WHERE minC2+1 <= maxC2
)
SELECT t1.C1,t1.minC2,t2.C3
FROM CTE t1 LEFT JOIN T t2 on t1.minC2 = t2.C2
ORDER BY C1,minC2;
| C1 | minC2 | C3 |
| --- | ----- | --- |
| 10 | 2 | T |
| 10 | 3 | E |
| 10 | 4 | |
| 10 | 5 | |
| 10 | 6 | S |
View on DB Fiddle

Answer 2

You can create a table of sequential numbers in your database, and then use an outer join to fill in the missing row values for C2.
It will be very useful for other queries as well, and takes very little space.
CREATE TABLE Numbers (Number INTEGER PRIMARY KEY);
INSERT INTO Numbers (Number) VALUES (1),(2),(3),(4),(5),(6) ...
And then:
SELECT T.C1, N.Number AS C2, T.C3
FROM Numbers AS N LEFT OUTER JOIN T ON T.C2 = N.Number
WHERE N.Number BETWEEN (SELECT MIN(C2) FROM T) AND (SELECT MAX(C2) FROM T)
ORDER BY C2;
HTH