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INFORMATION_SCHEMA.table_constraints

information_schema.table_constraints lists names of constraints (primary keys, foreign keys, unique values and checks) that are associated with a table. 
select * from information_schema.table_constraints where table_name = 'tabXYZ' and constraint_type = 'PRIMARY KEY';
select * from information_schema.table_constraints where table_name = 'tabXYZ' and constraint_type = 'FOREIGN KEY';
select * from information_schema.table_constraints where table_name = 'tabXYZ' and constraint_type = 'UNIQUE';
select * from information_schema.table_constraints where table_name = 'tabXYZ' and constraint_type = 'CHECK';

See also

Table constraints
referential_constraints
INFORMATION_SCHEMA

Index

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