Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE table_21168 ( "Date of Sterilization" text, "Age 10-19" real, "Age 20-29" real, "Age 30-39" real, "Age 40-49" real, "Age 50-59" real, "Age Unknown" real, "Total" real )

### Question ###
Name the least age 30-39 where age 20-29 is 593

### Accurate SQL ###

SELECT MIN("Age 30-39") FROM table_21168 WHERE "Age 20-29" = '593'