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MySQL pretreatment technology is what, many novices are not very clear about this, in order to help you solve this problem, the following editor will explain for you in detail, people with this need can come to learn, I hope you can gain something.

Traditional mysql processing flow

1. Prepare sql statements on the client side

2. Send sql statements to the MySQL server

3, execute the sql statement on the MySQL server

4, the server returns the execution result to the client

In this way, each sql statement is requested once, and the mysql server will receive and process it once. When a script file is executed repeatedly for the same statement, the pressure on the mysql server will increase, so there is mysql preprocessing to reduce the pressure on the server!

Basic strategies for preprocessing:

Force the sql statement into two:

The first part is the same command and structure as before.

The second part is the later variable data part.

When executing the sql statement, first send the same command and structure part to the MySQL server, let the MySQL server do a preprocessing in advance (at this time there is no real execution of the sql statement), and in order to ensure the structural integrity of the sql statement, the variable data parts are represented by a data placeholder when sending the sql statement for the first time! Like a question mark? Is a common data placeholder!

There are two forms of MySQL preprocessing: preprocessing with or without parameters

1. Preprocessing without parameters

First take a look at the data in the table!

1. Prepare the preprocessing statement

Prepare statement name from "preprocessed sql statement"

Prepare sql_1 from "select * from pdo"

2. Execute the preprocessing statement

Execute statement name

Execute sql_1

3. Delete preprocessing

Drop prepare statement name

Drop prepare sql_1

After deletion, the preprocessing statement can no longer be executed!

Second, pretreatment with parameters

1. Prepare the preprocessing statement

Prepare statement name from "preprocessed sql statement"

Prepare sql_2 from "select * from pdo where id =?"

2. Define parameter variables

Set @ variable name = value;-- where @ is a grammatical form for defining variables in MySQL (analogous to the $symbol in php)

Set @ id=2

3. Pass parameter variables and execute preprocessing statements

Execute statement name using parameter variable

Execute sql_2 using @ id;-- choose the message for id=2

4. Delete preprocessing

Drop prepare statement name

Drop prepare sql_2

Note: if there is more than one data placeholder, just pass the parameters in the order of the data placeholder:

Prepare sql_2 from "select * from pdo where id >? & & age >?"

Set @ id=2

Set @ age=30

Execute sql_2 using @ id,@age

Note that the unknown parameters here should correspond to the placeholders in step 1

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