SQL function summary

1. coalesce(null,1) If it is null return 1.
2. :: Two colons are used for type conversion
3. NUMERIC A data type is an exact numeric data type , Its precision is reserved to the least significant bit after arithmetic operation
4. to_chart(date,‘mm-dd’) Change the date to a character type in a certain format
5. to_date(‘2003-10-17 21:15:37’,‘yyyy-mm-dd’) Function to convert character type into date type in a certain format
6. ROUND(3.333,2) Function to round a numeric field to a specified number of decimal places .
7. floor() Round down to the specified number of decimal places
8. ceiling() Round up to the specified number of decimal places
9. sum(t.count) over() Continuous summation
10. postgresql extract(epoch from current_timestamp) Get the timestamp
11. postgresql generate_series(to_date(‘2013-04-03’,‘yyyy-mm-dd’), to_date(‘2013-04-06’,‘yyyy-mm-dd’), ‘1 day’) From small to large according to time , One day per step
12. split_part(‘string’, ‘,’ , 1) Cut according to the comma to return the first digit after cutting
13. substring (‘string’ , 2) Intercept string This field From 2 Character start
14. replace(‘string)’, ‘)’ , ‘’) Substitution function , Replace parentheses with blanks