1.ucase（）——把字段的值转换为大写
2.lcase（）——把字段的值转换为小写
3.mid()——从文本字段中提取字符
SELECT MID(column_name,start[,length]) FROM table_name
| column_name | 必需。要提取字符的字段。 |
| start | 必需。规定开始位置（起始值是 1）。 |
| length | 可选。要返回的字符数。如果省略，则 MID() 函数返回剩余文本。 |
4.len（）——返回文本字段中值的长度
5.round（）——把数值字段舍入为指定的小数位
SELECT ROUND(column_name,decimals) FROM table_name
| column_name | 必需。要舍入的字段。 |
| decimals | 必需。规定要返回的小数位数。 |
6.NOW ()——返回当前的日期和时间。
7.format（）——对字段的显示进行格式化。
SELECT FORMAT(column_name,format) FROM table_name
| column_name | 必需。要格式化的字段。 |
| format | 必需。规定格式。 |
总结：
| AND / OR | SELECT column_name(s) FROM table_name WHERE condition AND|OR condition |
| ALTER TABLE (add column) | ALTER TABLE table_name ADD column_name datatype |
| ALTER TABLE (drop column) | ALTER TABLE table_name DROP COLUMN column_name |
| AS (alias for column) | SELECT column_name AS column_alias FROM table_name |
| AS (alias for table) | SELECT column_name FROM table_name AS table_alias |
| BETWEEN | SELECT column_name(s) FROM table_name WHERE column_name BETWEEN value1 AND value2 |
| CREATE DATABASE | CREATE DATABASE database_name |
| CREATE INDEX | CREATE INDEX index_name ON table_name (column_name) |
| CREATE TABLE | CREATE TABLE table_name ( column_name1 data_type, column_name2 data_type, ....... ) |
| CREATE UNIQUE INDEX | CREATE UNIQUE INDEX index_name ON table_name (column_name) |
| CREATE VIEW | CREATE VIEW view_name AS SELECT column_name(s) FROM table_name WHERE condition |
| DELETE FROM | DELETE FROM table_name (Note: Deletes the entire table!!) or DELETE FROM table_name |
| DROP DATABASE | DROP DATABASE database_name |
| DROP INDEX | DROP INDEX table_name.index_name |
| DROP TABLE | DROP TABLE table_name |
| GROUP BY | SELECT column_name1,SUM(column_name2) FROM table_name GROUP BY column_name1 |
| HAVING | SELECT column_name1,SUM(column_name2) FROM table_name GROUP BY column_name1 HAVING SUM(column_name2) condition value |
| IN | SELECT column_name(s) FROM table_name WHERE column_name IN (value1,value2,..) |
| INSERT INTO | INSERT INTO table_name VALUES (value1, value2,....) or INSERT INTO table_name |
| LIKE | SELECT column_name(s) FROM table_name WHERE column_name LIKE pattern |
| ORDER BY | SELECT column_name(s) FROM table_name ORDER BY column_name [ASC|DESC] |
| SELECT | SELECT column_name(s) FROM table_name |
| SELECT * | SELECT * FROM table_name |
| SELECT DISTINCT | SELECT DISTINCT column_name(s) FROM table_name |
| SELECT INTO (used to create backup copies of tables) |
SELECT * INTO new_table_name FROM original_table_name or SELECT column_name(s) |
| TRUNCATE TABLE (deletes only the data inside the table) |
TRUNCATE TABLE table_name |
| UPDATE | UPDATE table_name SET column_name=new_value [, column_name=new_value] WHERE column_name=some_value |
| WHERE | SELECT column_name(s) FROM table_name WHERE condition |