Some Useful Functions in SQL

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combine two varchar

concat('a', 'b')
in group: group_concate(distinct name order by name separator ',')

upper case and lower case

upper('a') and lower('a')

select char in varchar

  1. select n char from left or right side left(name, n) or right(name, n)
  2. select all chars from nTH to mTH from the left substr(name, n, m)

length

length('aaaa')

agg functions

count(name)
in group also could use count(distinct name)

ROUND numbers

rounds a number to a specified number of decimal places
round(num, 2) or round(235.415, -1) = 240.000