sql总结

总结

• 查询的完整格式

    SELECT select_expr [,select_expr,...] [      
          FROM tb_name
          [WHERE 条件判断]
          [GROUP BY {col_name | postion} [ASC | DESC], ...] 
          [HAVING WHERE 条件判断]
          [ORDER BY {col_name|expr|postion} [ASC | DESC], ...]
          [ LIMIT {
    [offset,]rowcount | row_count OFFSET offset}]
    ]

• 完整的select语句

    select distinct *
    from 表名
    where ....
    group by ... having ...
    order by ...
    limit start,count

• 执行顺序为：
  • from 表名
  • where …
  • group by …
  • select distinct *
  • having …
  • order by …
  • limit start,count
• 实际使用中，只是语句中某些部分的组合，而不是全部