SQL

7.6    Temporal Functions

The topic of temporal functions covers date manipulations. In this section, we’ll inspect commonly used functions in this category.

7.6.1    Interval Calculations

As you would naturally expect, you can execute date calculations in DQL, where you add or subtract values to or from base dates. Listing 7.135 contains an example in which we add three days to req_dlv_date by using the INTERVAL keyword. Note that INTERVAL is followed by a natural language input, and PostgreSQL is able to handle that.

SELECT    id,    req_dlv_date,    req_dlv_date + INTERVAL  '3 days' AS dlv_date_deadlineFROM    customer_orderWHERE    req_dlv_date IS NOT NULL;  

Listing 7.135     Adding Three Days to Base Date

The results set can be seen in Table 7.124, which ...