what is the difference between unique and distinct in sql?
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The main difference between unique and distinct is that UNIQUE is a constraint that is used on the input of data and ensures data integrity. While DISTINCT keyword is used when we want to query our results or in other words, output the data.
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A primary key uniquely identifies a record in the relational database table, whereas a foreign key refers to the field in a table which is the primary key of another table.
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Primary Key is a unique and non-null key which identify a record uniquely in table. A table can have only one primary key. Candidate key is also a unique key to identify a record uniquely in a table but a table can have multiple candidate keys.
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The difference between Different and Distinct. When used as adjectives, different means not the same, whereas distinct means capable of being perceived very clearly. ... Different as an adjective: Distinct, separate; .
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Subqueries in the FROM Clause Columns in the subquery select list must have unique names. The columns in the subquery select list are available in the outer query just like columns of a table. The subquery can also be a query expression with UNION. Hive supports arbitrary levels of subqueries.
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As adjectives the difference between unique and specific is that unique is (not comparable) being the only one of its kind; unequaled, unparalleled or unmatched while specific is explicit or definite.
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The main difference between Custom SQL and Dynamic SQL is, in Custom SQL we can give the input values at design time. In Dynamic SQL we can give the input values at run time. By using custom SQL, one can execute any static SQL statements but by using dynamic we can able to execute only input field which query you set.
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INNER JOINs only look at the intersection of the results that meet the WHERE clause. FOR ALL ENTRIES eliminates duplicates from the results. I find JOINs to be more time consuming to code. (I can never find the “~” key.)
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The names of database objects need not be unique in a database. However, column names and index names must be unique within a table, and other object names must be unique for each owner within a database.
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['In the Navigation Pane, right-click the table that contains the field, and then click Design View.', 'Select the field that you want to make sure has unique values.']
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No. Every table should have some column (or set of columns) that uniquely identifies one and only one row. It makes it much easier to maintain the data. It's true, without a primary key (or some unique key), you don't have an insertion anomaly if you go to insert the same data multiple times.
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Counts the number of values in that field that aren't blank. Count (Distinct). Counts the number of different values in that field.
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There is two difference between them. 1. The not null constraint is by default added to primary key, it means, primary key attribute cannot accept null values, whereas, the attribute declared as unique can accept null values. It is the major difference between the two.
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Unique Key: It is a constraint which imposes limitation on database. ... Unique Index: It is a index which improves the performance while executing queries on your data base. In unique index it also not allows duplicate values in index . ie.no two rows will have the same index key value.
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Description. The SQL UNION operator is used to combine the result sets of 2 or more SELECT statements. It removes duplicate rows between the various SELECT statements. Each SELECT statement within the UNION must have the same number of fields in the result sets with similar data types.
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3 Answers. Well group by and distinct has its own use. Distinct is used to filter unique records out of the records that satisfy the query criteria. Group by clause is used to group the data upon which the aggregate functions are fired and the output is returned based on the columns in the group by clause.
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The difference between a UNIQUE constraint and a Primary Key is that per table you may only have one Primary Key but you may define more than one UNIQUE constraints. ... For MS SQL Server databases, a PRIMARY KEY will generate a unique CLUSTERED INDEX. A UNIQUE constraint will generate a unique NON-CLUSTERED INDEX.