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Database Developer Guide (API Version 2012-12-01)

Logical Conditions

Logical conditions combine the result of two conditions to produce a single result. All logical conditions are binary operators with a Boolean return type.

Syntax

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expression { AND | OR } expression NOT expression

Logical conditions use a three-valued Boolean logic where the null value represents an unknown relationship. The following table describes the results for logical conditions, where E1 and E2 represent expressions:

E1 E2 E1 AND E2 E1 OR E2 NOT E2
TRUE TRUE TRUE TRUE FALSE
TRUE FALSE FALSE TRUE TRUE
TRUE UNKNOWN UNKNOWN TRUE UNKNOWN
FALSE TRUE FALSE TRUE
FALSE FALSE FALSE FALSE
FALSE UNKNOWN FALSE UNKNOWN
UNKNOWN TRUE UNKNOWN TRUE
UNKNOWN FALSE FALSE UNKNOWN
UNKNOWN UNKNOWN UNKNOWN UNKNOWN

The NOT operator is evaluated before AND, and the AND operator is evaluated before the OR operator. Any parentheses used may override this default order of evaluation.

Examples

The following example returns USERID and USERNAME from the USERS table where the user likes both Las Vegas and sports:

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select userid, username from users where likevegas = 1 and likesports = 1 order by userid; userid | username --------+---------- 1 | JSG99FHE 67 | TWU10MZT 87 | DUF19VXU 92 | HYP36WEQ 109 | FPL38HZK 120 | DMJ24GUZ 123 | QZR22XGQ 130 | ZQC82ALK 133 | LBN45WCH 144 | UCX04JKN 165 | TEY68OEB 169 | AYQ83HGO 184 | TVX65AZX ... (2128 rows)

The next example returns the USERID and USERNAME from the USERS table where the user likes Las Vegas, or sports, or both. This query returns all of the output from the previous example plus the users who like only Las Vegas or sports.

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select userid, username from users where likevegas = 1 or likesports = 1 order by userid; userid | username --------+---------- 1 | JSG99FHE 2 | PGL08LJI 3 | IFT66TXU 5 | AEB55QTM 6 | NDQ15VBM 9 | MSD36KVR 10 | WKW41AIW 13 | QTF33MCG 15 | OWU78MTR 16 | ZMG93CDD 22 | RHT62AGI 27 | KOY02CVE 29 | HUH27PKK ... (18968 rows)

The following query uses parentheses around the OR condition to find venues in New York or California where Macbeth was performed:

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select distinct venuename, venuecity from venue join event on venue.venueid=event.venueid where (venuestate = 'NY' or venuestate = 'CA') and eventname='Macbeth' order by 2,1; venuename | venuecity ----------------------------------------+--------------- Geffen Playhouse | Los Angeles Greek Theatre | Los Angeles Royce Hall | Los Angeles American Airlines Theatre | New York City August Wilson Theatre | New York City Belasco Theatre | New York City Bernard B. Jacobs Theatre | New York City ...
Removing the parentheses in this example changes the logic and results of the query.

The following example uses the NOT operator:

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select * from category where not catid=1 order by 1; catid | catgroup | catname | catdesc -------+----------+-----------+-------------------------------------------- 2 | Sports | NHL | National Hockey League 3 | Sports | NFL | National Football League 4 | Sports | NBA | National Basketball Association 5 | Sports | MLS | Major League Soccer ...

The following example uses a NOT condition followed by an AND condition:

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select * from category where (not catid=1) and catgroup='Sports' order by catid; catid | catgroup | catname | catdesc -------+----------+---------+--------------------------------- 2 | Sports | NHL | National Hockey League 3 | Sports | NFL | National Football League 4 | Sports | NBA | National Basketball Association 5 | Sports | MLS | Major League Soccer (4 rows)

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