Thoughts caused by a Mysql statement _ MySQL-mysql tutorial

Thoughts on a Mysql statement bitsCN.com

Thoughts on a Mysql statement

Today, I saw a mysql statement written by my colleagues, but I didn't fully understand it. I suddenly felt the gap. in my mind, mysql statements only add, delete, query, and modify them, you can still write it like this.

[Php]

$ SQL = "SELECT category_general_table

FROM product_category

WHERE category_id IN

(SELECT DISTINCT

CAST (SUBSTRING (product_code, 1, 5) as unsigned) AS cid

FROM product_index

WHERE member_id = $ memberId AND shop_id = $ shopId )";

I have never written it like this CAST or SUBSTRI NG.

After checking the manual, another function CONVERT is similar to it.

Cast (value as type); Convert (value, type );

Not all types can be dropped. the type that can be converted is as follows:

Binary, with a BINARY prefix: binary

Character type, with parameters: CHAR ()

DATE: DATE

TIME: TIME

DATETIME type

Floating point: DECIMAL

Integer: SIGNED

UNSIGNED integer

It seems that I still have to read more manuals.

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