A primary key is a field in a database table that uniquely identifies each row/record. Primary keys must have distinct values. NULL values are not allowed in a primary key column. A table can only have one primary key, which can be made up of one or more fields.
The column or columns that hold values that uniquely identify each row in a table are known as primary keys. For Optim to insert, update, restore, or delete data from a database table, the table must contain a primary key. Optim makes use of database-defined primary keys.
Text and ntext columns cannot have a primary key. However, you may achieve the same functionality by using a varchar datatype (8000). The only difference is that this column can now hold up to 8000 characters.
A primary key is a field (or combination of fields) in a table that has values that are unique across all rows. Because each record has a unique value for the key, values of the key can be used to refer to whole records. There can only be one primary key per table.
A surrogate key is a one-of-a-kind identifier for a client's business entity or a database object. Natural keys cannot always be used to establish a unique table primary key. When a data modeller or architect chooses to use surrogate or helping keys for a table in the LDM, this is what happens.
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The course is very good. I have stuck at a point that how you create multiple rows with a single insert in sales.customer table. I get only one customer data. this table is related to bikestore data.
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very easy to understand SQL its was dream to learn SQL. Thanx for Learnvern
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