SQL Lesson 9: Queries with expressions

林秀吉

于 2018-04-23 01:05:43 发布

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Example query with expressions
SELECT particle_speed / 2.0 AS half_particle_speed
FROM physics_data
WHERE ABS绝对值(particle_position) * 10.0 > 500;

Select query with expression aliases
SELECT col_expression AS expr_description, …
FROM mytable;

为了编程方便，将复杂长的名字改为较短的字的表述

Example query with both column and table name aliases
SELECT column AS better_column_name, …
FROM a_long_widgets_table_name AS mywidgets
INNER JOIN widget_sales
  ON mywidgets.id = widget_sales.widget_id;

关于判断是否为整数

where xx%=0