Available in: DSQL, PSQL

Added in: 1.0

Changed in: 1.5

Description

A line starting with “–” (two dashes) is a comment and will be ignored. This also makes it easy to quickly comment out a line of SQL.

In Firebird 1.5 and up, the “–” can be placed anywhere on the line, e.g. after an SQL statement. Everything from the double dash to the end of the line will be ignored.

Example

a table to store our valued customers in:

create table Customers (
   name varchar(32),
   added_by varchar(24),
   custno varchar(8),
   purchases integer -- number of purchases
)

Notice that the second comment is only allowed in Firebird 1.5 and up.

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Available in: DSQL, PSQL, ESQL

Added in: IB

Description

When converting a string literal to a DATE, TIME or TIMESTAMP, Firebird allows the use of a shorthand “C-style” cast. This feature already existed in InterBase 6, but was never properly documented.

Syntax

datatype 'date/timestring'

Examples

update People set AgeCat = 'Old'
  where BirthDate < date '1-Jan-1943'

insert into Appointments
  (Employee_Id, Client_Id, App_date, App_time)

values
  (973, 8804, date 'today' + 2, time '16:00')
 
new.lastmod = timestamp 'now';

See also:

CAST

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Available in: DSQL, PSQL

Added in: 1.5

Description

A CASE construct returns exactly one value from a number of possibilities. There are two syntactic variants:

• The simple CASE, comparable to a Pascal case or a C switch.
• The searched CASE, which works like a series of if … else if … else if clauses.

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Syntax

CASE <expression>
   WHEN <exp1> THEN result1
   WHEN <exp2> THEN result2
   ...
   [ELSE defaultresult]
END

When this variant is used, <expression> is compared to <exp1>, <exp2> etc., until a match is found, upon which the corresponding result is returned. If there is no match and there is an ELSE clause, defaultresult is returned. If there is no match and no ELSE clause, NULL is returned.

The match is determined with the “=” operator, so if <expression> is NULL, it won't match any of the <expN>s, not even those that are NULL.

The results don't have to be literal values: they may also be field or variable names, compound expressions, or NULL literals.

Example

select name,
       age,
       case upper(sex)
          when 'M' then 'Male'
          when 'F' then 'Female'
          else 'Unknown'
       end,
       religion
 from people

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Syntax

CASE
   WHEN <bool_exp1> THEN result1
   WHEN <bool_exp2> THEN result2
   ...
  [ELSE defaultresult]
END

Here, the <bool_expN>s are tests that give a ternary Boolean result: true, false, or NULL. The first expression evaluating to TRUE determines the result. If no expression is TRUE and there is an ELSE clause, defaultresult is returned. If no expression is TRUE and there is no ELSE clause, NULL is returned.

As with the simple CASE, the results don't have to be literal values: they may also be field or variable names, compound expressions, or NULL literals.

Example

CanVote = case
             when Age >= 18 then 'Yes'
             when Age < 18 then 'No'
             else 'Unsure'
          end;