How to assign default values ​​to fields when querying MySQL

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When querying a field, you need to give the same value to a field.

You can hard-code this value or get it from the database

1. Hard-coded values

SELECT
 mfr_id AS mfrId,
 mfr_name AS mfrName,
 IFNULL(NULL, 587694978080178176) AS suppId
FROM
 mater_prod materProd

Query results

2. Get values ​​from the database

SELECT
 mfr_id AS mfrId,
 mfr_name AS mfrName,
 IFNULL(NULL, mfr_id) AS suppId
FROM
 mater_prod materProd

Query results

Supplementary knowledge: How to set a default value if the mysql query field is empty

In common cases, the following is to calculate inventory. If the inventory or locked inventory is empty, the default value is 0.

SELECT
(IFNULL(t_inventory.pro_number,0)-IFNULL(t_inventory.locked_number,0)) AS content_number
FROM
t_inventory

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