8. Performant SQL

Activity 8.01: Query Planning

Solution:

1. Open PostgreSQL with psql and connect to the sqlda database.
2. Use the EXPLAIN command to return the query plan for selecting all available records within the customers table:

   EXPLAIN 
   SELECT * 
   FROM customers;

3. Read the output of the plan and determine the total query cost, the setup cost, the number of rows to be returned, and the width of each row.

The output is as follows:

Seq Scan on customers  (cost=0.00..1535.00 rows=50000 width=140)

As such, the total query cost is 1535.00, the setup cost is 0.00, the number of rows to be returned is 50000, and the width of each row is 140. Your result may have numbers that are slightly different. But the general concept of measurements should be the same.

4. Repeat the query from step 2 of this activity, this time limiting the number of returned records to 15. Review the updated query plan and compare its output against the output of the previous step...