A primary key\u2019s main features are:<\/p>\n
- \n
- It must contain a unique value for each row of data. A table can have only one primary key constraint<\/li>\n
- It cannot contain null values.<\/li>\n
- Every row must have a primary key value.<\/li>\n
- It enforces the entity integrity of data.<\/li>\n
- Primary key always has a unique data.<\/li>\n
- Primary key length cannot be more than 900 bytes.<\/li>\n
- Primary key cannot have a null value.<\/li>\n
- Duplicate values are not allowed in primary key.<\/li>\n
- A primary key might use one or more fields already present in the table, or a unique field can be created to be the primary key.<\/li>\n<\/ul>\n
![\"\"](\"https:\/\/www.wikitechy.com\/interview-questions\/wp-content\/uploads\/2022\/08\/primary-key.png\")
<\/p>\n","protected":false},"excerpt":{"rendered":"In relational database primary key is a specific choice of minimal set of attributes that uniquely specify a relation. Primary key is a special realational database table column key that uniquely identifies a table record. In a table if primary key needs to be created then we have to define a primary key constraint when […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"passster_activate_protection":false,"passster_protect_child_pages":"","passster_protection_type":"password","passster_password":"","passster_activate_overwrite_defaults":"","passster_headline":"","passster_instruction":"","passster_placeholder":"","passster_button":"","passster_id":"","passster_activate_misc_settings":"","passster_redirect_url":"","passster_hide":"no","passster_area_shortcode":"","gtb_hide_title":false,"gtb_wrap_title":false,"gtb_class_title":"","gtb_remove_headerfooter":false,"footnotes":""},"categories":[6547],"tags":[18543,18544,18535,18533,18524,18537,18538,18539,18529,18541,18542,18526,18531,18528,18540,18532,18527,18525,18530,18534,18536],"class_list":["post-4831","post","type-post","status-publish","format-standard","hentry","category-sql","tag-define-what-is-a-primary-key","tag-postgres-what-is-a-primary-key","tag-primary-key-example","tag-what-is-a-foreign-key","tag-what-is-a-primary-key","tag-what-is-a-primary-key-and-explain-its-characteristics","tag-what-is-a-primary-key-and-foreign-key","tag-what-is-a-primary-key-and-foreign-key-in-sql","tag-what-is-a-primary-key-class","tag-what-is-a-primary-key-example","tag-what-is-a-primary-key-explain","tag-what-is-a-primary-key-in-a-database","tag-what-is-a-primary-key-in-a-relational-database","tag-what-is-a-primary-key-in-access","tag-what-is-a-primary-key-in-computer","tag-what-is-a-primary-key-in-dbms","tag-what-is-a-primary-key-in-mysql","tag-what-is-a-primary-key-in-sql","tag-what-is-a-primary-key-used-for-in-a-database","tag-what-is-primary-key-and-foreign-key","tag-what-is-primary-key-in-ms-access"],"yoast_head":"\n
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