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45 lines
2.5 KiB
45 lines
2.5 KiB
2 years ago
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---
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title: "Primary Key"
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description: "Primary Key"
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position: 574
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category: "Product"
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menuTitle: "Primary Key"
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---
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## What is a Primary Key ?
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- Key in a relational database table that is unique for each record
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## What is the use of Primary Key ?
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- As it uniquely identifies an individual record of a table, it is used internally by NocoDB for all operations associated with a record
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## Primary Key in NocoDB
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- Primary Key that gets defined / used in NocoDB depends on how underlying table was created. Summary is captured below
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1. From UI, Create new table / Import from Excel / Import from CSV
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1. An `ID` [datatype: Integer] system field created by default during table creation is used as primary key
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2. Additional system fields `created-at`, `updated-at` are inserted by default & can be omitted optionally; these fields can be deleted after table creation
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2. Connect to existing external database
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1. Existing `primary key` field defined for a table is retained as is; NocoDB doesn't insert a new ID field
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2. Additional system fields `created-at`, `updated-at` are not inserted by default
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3. Import from Airtable
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1. Airtable record ID is marked as primary key for imported records, and is mapped to field `ncRecordId` [datatype: varchar]
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2. If a new record is inserted after migration & if ncRecordId field was omitted during record insertion - auto generated string will be inserted by NocoDB
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3. Computed hash value for the entire record is stored in system field `ncRecordHash`
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4. Additional system fields `created-at`, `updated-at` are not inserted by default
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4. Create new table using SDK / API
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1. No default primary key field is introduced by NocoDB. It has to be explicitly specified during table creation (using attribute `pk: true`)
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## What if Primary Key was missing?
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It is possible to have a table without any primary key.
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- External database table can be created without primary key configuration.
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- New table can be created using SDK / API without primary key
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In such scenario's, new records can be created in NocoDB for this table, but records can't be updated or deleted [as there is now way for NocoDB to uniquely identify these records]
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#### Example : Primary Key & optional system fields during new table creation
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#### Example : Show System Fields
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## Can I change the Primary Key to another column within tables ?
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- You can't update Primary Key from NocoDB UI. You can reconfigure it at database level directly & trigger `metasync` explicitly
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