Re: Check constraints do not seem to be working!!!
Thanks Laurenz This is interesting...b is True Thanks and regards, Jitendra On Wed 11 Nov, 2020, 22:52 Laurenz Albe, wrote: > On Wed, 2020-11-11 at 11:47 +0100, Tomas Vondra wrote: > > you may do this, for example: > > > > (b it not null and b = true) and (c is not null) > > > > Or something like that. > > My (equivalent) suggestion: > >b IS TRUE AND c IS NOT NULL > > Yours, > Laurenz Albe > -- > Cybertec | https://www.cybertec-postgresql.com > >
Re: Check constraints do not seem to be working!!!
On Wed, 2020-11-11 at 11:47 +0100, Tomas Vondra wrote: > you may do this, for example: > > (b it not null and b = true) and (c is not null) > > Or something like that. My (equivalent) suggestion: b IS TRUE AND c IS NOT NULL Yours, Laurenz Albe -- Cybertec | https://www.cybertec-postgresql.com
Re: Check constraints do not seem to be working!!!
Thanks Tomas Understood... My bad Was just not looking at that aspect Thanks once again, Regards, Jitendra On Wed, 11 Nov 2020 at 16:17, Tomas Vondra wrote: > > On 11/11/20 10:06 AM, Jitendra Loyal wrote: > > Thanks Nikolay > > > > I read that but is there a way to meet the above requirement. And I will > > like to add that IS NULL and IS NOT NULL should evaluate to true/false. > > These operators are made for this and should not be returning NULL. > > > > This has nothing to do with IS [NOT] NULL, it's the first part of the > expression (b = TRUE) causing trouble. Essentially, the constraint > > (b = true) and (c is not null) > > is evaluated in two steps. First we evaluate the two parts individually, > and for (null, true) the results would look like this: > > (b = true) => null > (c is not null) => true > > and then we combine those results using 'AND' > > null AND true => null > > which is considered as if the constraint matches. If you want to handle > NULL for the first expression, you may do this, for example: > > (b it not null and b = true) and (c is not null) > > Or something like that. > > > regards > > -- > Tomas Vondra > EnterpriseDB: http://www.enterprisedb.com > The Enterprise PostgreSQL Company >
Re: Check constraints do not seem to be working!!!
On 11/11/20 10:06 AM, Jitendra Loyal wrote: > Thanks Nikolay > > I read that but is there a way to meet the above requirement. And I will > like to add that IS NULL and IS NOT NULL should evaluate to true/false. > These operators are made for this and should not be returning NULL. > This has nothing to do with IS [NOT] NULL, it's the first part of the expression (b = TRUE) causing trouble. Essentially, the constraint (b = true) and (c is not null) is evaluated in two steps. First we evaluate the two parts individually, and for (null, true) the results would look like this: (b = true) => null (c is not null) => true and then we combine those results using 'AND' null AND true => null which is considered as if the constraint matches. If you want to handle NULL for the first expression, you may do this, for example: (b it not null and b = true) and (c is not null) Or something like that. regards -- Tomas Vondra EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company
Re: Check constraints do not seem to be working!!!
On 11 Nov 2020, at 11:15, Jitendra Loyal wrote: > > > Thanks Nikolay > > I read that but is there a way to meet the above requirement. And I will like > to add that IS NULL and IS NOT NULL should evaluate to true/false. These > operators are made for this and should not be returning NULL. That is exactly what they do. Your problem is with the equality operator and its behaviour with NULL values, which is described in the referenced document. -- If you can't see the forest for the trees, Cut the trees and you'll find there is no forest. >> On Wed 11 Nov, 2020, 14:18 Nikolay Samokhvalov, >> wrote: >>> On Wed, Nov 11, 2020 at 12:26 AM Jitendra Loyal >>> wrote: >>> Despite the above two constraints, the following rows get into the table: >>> insert into t (b , c) values (null, true), (null, false); >> >> This behavior is described in the docs >> https://www.postgresql.org/docs/current/ddl-constraints.html#DDL-CONSTRAINTS-CHECK-CONSTRAINTS: >> >> > It should be noted that a check constraint is satisfied if the check >> > expression evaluates to true or the null value. Since most expressions >> > will evaluate to the null value if any operand is null, they will not >> > prevent null values in the constrained columns. To ensure that a column >> > does not contain null values, the not-null constraint described in the >> > next section can be used.
Re: Check constraints do not seem to be working!!!
Thanks Nikolay I read that but is there a way to meet the above requirement. And I will like to add that IS NULL and IS NOT NULL should evaluate to true/false. These operators are made for this and should not be returning NULL. Regards, Jitendra On Wed 11 Nov, 2020, 14:18 Nikolay Samokhvalov, wrote: > On Wed, Nov 11, 2020 at 12:26 AM Jitendra Loyal > wrote: > >> Despite the above two constraints, the following rows get into the table: >> insert into t (b , c) values (null, true), (null, false); >> > > This behavior is described in the docs > https://www.postgresql.org/docs/current/ddl-constraints.html#DDL-CONSTRAINTS-CHECK-CONSTRAINTS > : > > > It should be noted that a check constraint is satisfied if the check > expression evaluates to true or the null value. Since most expressions will > evaluate to the null value if any operand is null, they will not prevent > null values in the constrained columns. To ensure that a column does not > contain null values, the not-null constraint described in the next section > can be used. >
Re: Check constraints do not seem to be working!!!
On Wed, Nov 11, 2020 at 12:26 AM Jitendra Loyal wrote: > Despite the above two constraints, the following rows get into the table: > insert into t (b , c) values (null, true), (null, false); > This behavior is described in the docs https://www.postgresql.org/docs/current/ddl-constraints.html#DDL-CONSTRAINTS-CHECK-CONSTRAINTS : > It should be noted that a check constraint is satisfied if the check expression evaluates to true or the null value. Since most expressions will evaluate to the null value if any operand is null, they will not prevent null values in the constrained columns. To ensure that a column does not contain null values, the not-null constraint described in the next section can be used.
Re: Check constraints do not seem to be working!!!
st 11. 11. 2020 v 9:38 odesílatel Chris Sterritt napsal: > > On 11/11/2020 06:44, Jitendra Loyal wrote: > > Consider this table definition: > create table t ( i serial, b bool, c bool, > constraint b_c check ( (b = true and c is > not null ) or (b is distinct > from true and c is null) ) > constraint b_c check ( (b = true and c is > not null ) or (b = false and c > is null) or (b is null and c is null) ) > ); > Despite the above two constraints, the following rows get into the table: > insert into t (b , c) values (null, true), (null, false); > > > (b = TRUE AND c IS NOT NULL) evaluates to null when b is null > > yes, constraint is violated only when result is false, no when it is null. Regards Pavel > Cheers, > Chris Sterritt > >
Re: Check constraints do not seem to be working!!!
On 11/11/2020 06:44, Jitendra Loyal wrote: Consider this table definition: create table t ( i serial, b bool, c bool, constraint b_c check ( (b = true and c is not null ) or (b is distinct from true and c is null) ) constraint b_c check ( (b = true and c is not null ) or (b = false and c is null) or (b is null and c is null) ) ); Despite the above two constraints, the following rows get into the table: insert into t (b , c) values (null, true), (null, false); (b =TRUE AND c IS NOT NULL) evaluates to null when b is null Cheers, Chris Sterritt
Check constraints do not seem to be working!!!
Consider this table definition: create table t ( i serial, b bool, c bool, constraint b_c check ( (b = true and c is not null ) or (b is distinct from true and c is null) ) constraint b_c check ( (b = true and c is not null ) or (b = false and c is null) or (b is null and c is null) ) ); Despite the above two constraints, the following rows get into the table: insert into t (b , c) values (null, true), (null, false);
