Use of comment keyword in database

COMMENT Introduction to the use of

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effect ： Add a comment to a field or column .

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1. Add comments to fields when creating tables

CREATE TABLE emp(
    emp_id INT PRIMARY KEY AUTO_INCREMENT COMMENT ' Number ',
    emp_name CHAR(20) NOT NULL DEFAULT '' COMMENT ' full name ',
    salary DECIMAL(10,2) NOT NULL DEFAULT 0 COMMENT ' Wages ',
    department CHAR(20) NOT NULL DEFAULT '' COMMENT ' department '
);

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2. Add comments to the fields after creating the table

ALTER TABLE emp CHANGE COLUMN department department CHAR(20) NOT NULL DEFAULT '' COMMENT ' department ';

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3. View comments for all fields in the table

• The way 1

show full columns from tablename;

SHOW FULL COLUMNS FROM emp;

• The way 2

SELECT * FROM COLUMNS WHERE TABLE_SCHEMA='dbname' AND TABLE_NAME='tablename';

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4. Add comments to the table when creating it

CREATE TABLE test(
    field_name INT
)COMMENT=" The comment ";

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5. Add comments to the table after it is created

alter table tablename comment ' Table notes ';

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6. See table notes

• The way 1

show create table tablename;

• The way 2

USE information_schema;
SELECT * FROM TABLES WHERE TABLE_SCHEMA='dbname' AND TABLE_NAME='tablename';

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