Python 学习笔记：Basic SQL

这里主要是整理 SQL 一些基础的“增删查改”的语法，方便自己不记得的时候可以快速查找。

SELECT Statement

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/* general syntax */
SELECT column1, column2, ... FROM table1;

/* retrieve all columns */
SELECT * FROM table1;

/* filter result or get specific data */
SELECT * FROM table1 WHERE condition;

/* retrieve the number of rows */
SELECT COUNT(*) FROM table1;

/* retrieve the number of some values */
SELECT COUNT(column1) FROM table1 WHERE condition;

/* retrieve some values without repeated items */
SELECT DISTINCT column1 FROM table1;

/* retrieve the number of some values without repeated items */
SELECT COUNT(DISTINCT column1) FROM table1 WHERE condition;

/* retrieve the first n rows from the table */
SELECT * FROM table1 LIMIT n;

/* retrieve the first n rows from the table starting from row m */
SELECT * FROM table1 LIMIT n OFFSET m;

INSERT, UPDATE, DELETE Statement

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/* general syntax */

INSERT INTO table1 (column1, column2, ...) VALUES (value1, value2, ... );

UPDATE table1 SET column1 = value1, column2 = value2, ... WHERE condition;

DELETE FROM table1 WHERE condition;

CREATE Statement

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/* general syntax */
CREATE TABLE table1 (column1 datatype, column2 datatype, column3 datatype, ...);

ALTER Statement

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/* add column */
ALTER TABLE table1 ADD COLUMN column1 datatype constraint;

/* delete column */
ALTER TABLE table1 DROP COLUMN column1;

/* change column data type */
ALTER TABLE table1 ALTER COLUMN column1 SET DATA TYPE datatype

/* rename column */
ALTER TABLE table1 RENAME COLUMN name1 TO name2;

TRUNCATE, DROP Statement

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/* clear table */
TRUNCATE TABLE table1;

/* delete table */
DROP TABLE table1;