In MySQL, add and remove fields in SQL, modify field names, field types, comments, and adjust Field order summary

1. Add a field

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Add a field, the default is empty ALTER TABLE user add COLUMN new1 VARCHAR DEFAULT NULL; Add a field, default cannot be empty ALTER TABLE user add COLUMN new2 VARCHAR is not NULL;

2. How to add the field in bulk

Method One
You can use transactions here

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Bagin;                                             //Transaction start ALTER TABLE em_day_data add F_DAY_HOUSE7 int (one); ALTER TABLE Em_day _data add F_day_house8 int (11); ALTER TABLE em_day_data add F_DAY_HOUSE9 int (11); ALTER TABLE em_day_data add F_DAY_HOUSE10 int (11); commit;                                              //COMMIT TRANSACTION, transaction end

A transaction (transaction) is a program execution unit consisting of a series of sequence of operations, either done or not, and is an indivisible unit of work.

Method Two
MySQL Batch add multiple fields to a table
ALTER TABLE name Add (field 1 type (length), field 2 type (length), field 3 type (length));

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ALTER TABLE Em_day_data Add (f_day_house11 int (one), F_day_house12 Int (one), F_day_house13 Int (11));

3. Delete a field

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Delete a field ALTER TABLE user DROP COLUMN new2;

4. Modify a field

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Modify the type of a field ALTER TABLE user MODIFY New1 VARCHAR (10); To modify the name of a field, be sure to reassign the field's type now ALTER TABLE user change new1 new4 int;

5. Batch Modify field name

The code is as follows

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ALTER TABLE change field name int (one) not null before field name modification The field name Int (one) is not null when the field name is modified before change modification The field name Int (one) is not null when the field name is modified before change modification The field name Int (one) is not null when the field name is modified before change modification change field name Int (one) not NULL when field name is modified before change

Example:

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ALTER TABLE em_day_data change f_day_house11 f_day_hour11 Int (one) not NULL, Change F_day_house12 f_day_hour12 Int (one) not NULL, Change F_day_house13 F_day_hour13 Int (one) not NULL, Change F_day_house14 f_day_hour14 Int (one) not NULL, Change F_day_house15 f_day_hour15 Int (one) not NULL, Change F_day_house16 f_day_hour16 Int (one) not NULL, Change F_day_house17 f_day_hour17 Int (one) NOT NULL

6, add comments

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You can add a comment to a table ALTER TABLE ' table_name ' COMMENT ' annotation '; Add a comment to a field, which also applies to modifying ALTER TABLE ' table_name ' change ' column_name ' column_name ' type (longth) UNSIGNED null DEFAULT null COMMENT ' annotations '

7, adjust the field order:

ALTER TABLE name
Change field name new field name segment type default value after field name (after which field is skipped)
Example:

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ALTER TABLE appstore_souapp_app_androidmarket; Change getpricecurrency getpricecurrency varchar (m) default null after GetPrice;