UPDATE FROM another table value with CASE SUBSTRING and WHERE - mysql

Question

I tried to update my main table --> budget with values from item_master table with condition
Here's the table structure
budget :
+-------------------+---------------+------+-----+------------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------------------+---------------+------+-----+------------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| department | varchar(50) | YES | | NULL | |
| section | varchar(50) | YES | | NULL | |
| budget_id | varchar(50) | NO | | NULL | |
| carmaker | varchar(255) | YES | | NULL | |
| carline | varchar(255) | YES | | NULL | |
| phase | varchar(255) | YES | | NULL | |
| purpose | varchar(50) | YES | | NULL | |
| order_plan | varchar(50) | YES | | NULL | |
| required_date | varchar(50) | YES | | NULL | |
| subgroup | varchar(255) | YES | | NULL | |
| item_desc | varchar(255) | YES | | NULL | |
| item_code | varchar(255) | YES | | NULL | |
| qty | int(11) | YES | | NULL | |
| curr | char(3) | YES | | NULL | |
| price | decimal(20,2) | YES | | NULL | |
| amount_ori | decimal(20,2) | YES | | NULL | |
| amount | decimal(20,2) | YES | | NULL | |
| amount_reduce_ori | decimal(20,2) | NO | | NULL | |
| amount_reduce_usd | decimal(20,2) | NO | | NULL | |
| qty_reduce | decimal(20,2) | NO | | NULL | |
| qty_final | int(11) | YES | | NULL | |
| amount_final | decimal(20,2) | YES | | NULL | |
| status | varchar(50) | YES | | uncommited | |
| source | varchar(50) | YES | | NULL | |
| coa_production | char(7) | YES | | NULL | |
| coa_general | char(7) | YES | | NULL | |
| hfm_cr | char(6) | YES | | NULL | |
| hfm_pl | char(6) | YES | | NULL | |
| update_record | varchar(50) | YES | | NULL | |
| user | varchar(50) | YES | | NULL | |
+-------------------+---------------+------+-----+------------+----------------+
item_master :
+----------------+---------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+----------------+---------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| subgroup | varchar(255) | NO | | NULL | |
| item_desc | varchar(255) | NO | | NULL | |
| item_code | varchar(255) | NO | | NULL | |
| uom | varchar(255) | NO | | NULL | |
| price | decimal(20,2) | NO | | NULL | |
| coa_production | char(7) | NO | | NULL | |
| coa_general | char(7) | NO | | NULL | |
| hfm_cr | varchar(50) | NO | | NULL | |
| hfm_pl | varchar(50) | NO | | NULL | |
+----------------+---------------+------+-----+---------+----------------+
I'm trying to get coa_production or coa general , depend on purpose field
if the first three (3) characters = 'PRO' then use coa_production, else use coa_general with item_code as the unique string/foreign keys
Here's my current code :
UPDATE budget CASE
WHEN SUBSTR(purpose,1,3) = 'PRO' THEN
SET coa_production = (SELECT coa_production FROM item_master WHERE budget.item_code = item_master.item_code) ELSE
SET coa_general = (SELECT coa_general FROM item_master WHERE budget.item_code = item_master.item_code) END
my goal is when purpose = 'PRO' then the only field that has to be filled is coa_production using the value from item_master table, so does if purpose = 'GEN' then the only field that has to be filled is coa_general

Answer 1

I would express this using an update join:
UPDATE budget b
LEFT JOIN item_master im
ON b.item_code = im.item_code
SET
b.coa_production = CASE WHEN LEFT(b.purpose, 3) = 'PRO' THEN im.coa_production END,
b.coa_general = CASE WHEN LEFT(b.purpose, 3) = 'GEN' THEN im.coa_general END
WHERE
LEFT(b.purpose, 3) IN ('PRO', 'GEN');
Note that a left join (rather than an inner join) is required here, to keep the behavior the same as your original query. Using a left join, a NULL would be assigned to a column which did not find any matching record in the item_master table.