COUNT Function
COUNT(*), COUNT(1), COUNT(column_name)
COUNT(*): 统计所有行，不管是否为NULLCOUNT(1): 统计所有代码行，不管是否为NULLCOUNT(column_name): 统计指定列的行数，判断是否为NULL
Speed
COUNT(*)和COUNT(1)的速度是一样的，因为COUNT(*)会统计所有列，而COUNT(1)会统计所有代码行COUNT(*)是SQL92定义的标准统计数的语法，所以速度会快一些COUNT(column_name)会判断是否为NULL，所以速度会慢一些
USING Function
The USING clause is used to specify some condition to join tables.
sql
SELECT * FROM table1 JOIN table2 USING (column_name);
-- equal to
SELECT * FROM table1 JOIN table2 ON table1.column_name = table2.column_name;ORDER BY Clause
ORDER BY 1
order by the first column in the select list.
sql
SELECT * FROM table_name ORDER BY 1;
SELECT first_column, second_column FROM table_name ORDER BY 1;JOIN Clause
JOIN Cheat Sheet
Reference
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