MySQL 8.0

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CREATE TABLE tb_kse(id_no INT, ss_no INT, gen_col INT GENERATED ALWAYS AS (ifnull(ss_no, id_no)) STORED )
create index IDX_KSE_NO_01 on tb_kse(ifnull(ss_no, id_no));

You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'ss_no, id_no))' at line 1


create index IDX_KSE_NO_01 on tb_kse(gen_col);

Records: 0  Duplicates: 0  Warnings: 0


explain
SELECT *
FROM tb_kse
WHERE gen_col = 10;


id
select_type
table
partitions
type
possible_keys
key
key_len
ref
rows
filtered
Extra


1
SIMPLE
tb_kse
null
ref
IDX_KSE_NO_01
IDX_KSE_NO_01
5
const
1
100.00
null