1, Table field

see

• Check the contents of the table , Field type , Field description, etc
  describe TableName

conditional

Null Judge

• NVL(X, Y)/ ifnull(X, Y)/isnull(X, Y)
  When X Not NULL When to return to X Value , Otherwise return to Y Value .
• coalesce(X, Y, Z, ...)
  Returns the first non in the input parameter NULL value , If all input parameters are NULL, Then return to NULL.
• nullif(X, Y)
  If two expressions are equal , Then return to NULL. If two expressions are not equal , Returns the value of the first expression . The data types of the two expressions must remain compatible . in addition , The first expression cannot be null NULL, If it is NULL, Will never match the second expression .
  This function is usually used in division expressions to prevent the divisor from being zero . for example select 1.0 /nullif(expr,0) as rate from table_xxxxx

Numerical expression

• nullifzero(numeric expr)
  If the expression is 0, Then return to NULL; If the expression is non-zero , Returns the expression itself . The return type is the same as the original return value type . If the return value is an integer, it will be promoted to BIGINT type , if FLOAT Type I will be promoted to DOUBLE type . If the corresponding column is not allowed to be like BIGINT perhaps DOUBLE Such a high-precision type , Need to use CAST() Function to cast .
• zeroifnull(numeric expr)
  If the expression is NULL, Then return to 0, If the expression is not NULL, Returns the expression itself . Note that the expression type should be numeric.

Boolean value

• if(boolean expression , Return value when true , False or null Return value at time )
• istrue(boolean), isfalse(boolean), isnottrue(boolean), isnotfalse(boolean)

To choice

• case when ... then ... [else when ... then ...] else ... end

Mathematical functions

Type conversion

• cast(X as type)
  Type conversion
• to_date(string)
  String to date

Statistics

• NDV()
  Returns a value similar to COUNT(DISTINCT col ) The approximate value of the result .

2, Lookup table

Find all tables containing some strings in the stock out

show tables in DataBase like '*abc*'

3, Table partitioning

Check the partition

show partitions TableName;

Reference resources ：
https://blog.csdn.net/zy103118/article/details/101028394