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Fix small typos in README.md (#44)

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0xflotus 2023-01-10 10:20:27 +01:00 committed by GitHub
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@ -88,7 +88,7 @@ create_immv(immv_name text, view_definition text) RETURNS bigint
```
`create_immv` defines a new IMMV of a query. A table of the name `immv_name` is created and a query specified by `view_definition` is executed and used to populate the IMMV. The query is stored in `pg_ivm_immv`, so that it can be refreshed later upon incremental view maintenance. `create_immv` returns the number of rows in the created IMMV.
When an IMMV is created, some triggers are automatically created so that the view's contents are immediately updated when its base tables are modified. In addition, a unique index is created on the IMMV automatically if possible. If the view definition query has a GROUP BY clause, a unique index is created on the columns of GROUP BY expressions. Also, if the view has DISTINCT clause, a unique index is created on all columns in the target list. Otherwise, if the IMMV contains all primary key attritubes of its base tables in the target list, a unique index is created on these attritubes. In other cases, no index is created.
When an IMMV is created, some triggers are automatically created so that the view's contents are immediately updated when its base tables are modified. In addition, a unique index is created on the IMMV automatically if possible. If the view definition query has a GROUP BY clause, a unique index is created on the columns of GROUP BY expressions. Also, if the view has DISTINCT clause, a unique index is created on all columns in the target list. Otherwise, if the IMMV contains all primary key attributes of its base tables in the target list, a unique index is created on these attributes. In other cases, no index is created.
#### refresh_imm
@ -173,7 +173,7 @@ test=# SELECT * FROM immv WHERE aid = 1;
An appropriate index on IMMV is necessary for efficient IVM because we need to looks for tuples to be updated in IMMV. If there are no indexes, it will take a long time.
Therefore, when an IMMV is created by the `create_immv` function, a unique index is created on it automatically if possible. If the view definition query has a GROUP BY clause, a unique index is created on the columns of GROUP BY expressions. Also, if the view has DISTINCT clause, a unique index is created on all columns in the target list. Otherwise, if the IMMV contains all primary key attritubes of its base tables in the target list, a unique index is created on these attritubes. In other cases, no index is created.
Therefore, when an IMMV is created by the `create_immv` function, a unique index is created on it automatically if possible. If the view definition query has a GROUP BY clause, a unique index is created on the columns of GROUP BY expressions. Also, if the view has DISTINCT clause, a unique index is created on all columns in the target list. Otherwise, if the IMMV contains all primary key attributes of its base tables in the target list, a unique index is created on these attributes. In other cases, no index is created.
In the previous example, a unique index "immv_index" is created on aid and bid columns of "immv", and this enables the rapid update of the view. Dropping this index make updating the view take a loger time.