Post #1722

Here are some essential SQL tips for beginners 👇👇 ◆ Primary Key = Unique Key + Not Null constraint ◆ To perform case insensitive search use UPPER() function ex. UPPER(customer_name) LIKE ‘A%A’ ◆ LIKE operator is for string data type ◆ COUNT(*), COUNT(1), COUNT(0) all are same ◆ All aggregate functions ignore the NULL values ◆ Aggregate functions MIN, MAX, SUM, AVG, COUNT are for int data type whereas STRING_AGG is for string data type ◆ For row level filtration use WHERE and aggregate level filtration use HAVING ◆ UNION ALL will include duplicates where as UNION excludes duplicates ◆ If the results will not have any duplicates, use UNION ALL instead of UNION ◆ We have to alias the subquery if we are using the columns in the outer select query ◆ Subqueries can be used as output with NOT IN condition. ◆ CTEs look better than subqueries. Performance wise both are same. ◆ When joining two tables , if one table has only one value then we can use 1=1 as a condition to join the tables. This will be considered as CROSS JOIN. ◆ Window functions work at ROW level. ◆ The difference between RANK() and DENSE_RANK() is that RANK() skips the rank if the values are the same. ◆ EXISTS works on true/false conditions. If the query returns at least one value, the condition is TRUE. All the records corresponding to the conditions are returned. Like for more 😄😄