Which query is based on more than one table?
Wildcard tables enable you to query multiple tables using concise SQL statements. Wildcard tables are available only in Google Standard SQL. For equivalent functionality in legacy SQL, see Table wildcard functions. Show
A wildcard table represents a union of all the tables that match the wildcard expression. For example, the following
Each row in the wildcard table contains a special column, For information on wildcard table syntax, see Wildcard tables in the Google Standard SQL reference. LimitationsWildcard table queries are subject to the following limitations.
Before you begin
When to use wildcard tablesWildcard tables are useful when a dataset contains multiple, similarly named tables that have compatible schemas. Typically, such datasets contain tables that each represent data from a single day, month, or year. For example, a public dataset hosted by BigQuery, the NOAA Global Surface Summary of the Day Weather Data, contains a table for each year from 1929 through the present. A query that scans all the table IDs from 1929 through 1940 would be very long if you have to name all 12 tables in the #standardSQL SELECT max, ROUND((max-32)*5/9,1) celsius, mo, da, year FROM ( SELECT * FROM `bigquery-public-data.noaa_gsod.gsod1929` UNION ALL SELECT * FROM `bigquery-public-data.noaa_gsod.gsod1930` UNION ALL SELECT * FROM `bigquery-public-data.noaa_gsod.gsod1931` UNION ALL # ... Tables omitted for brevity SELECT * FROM `bigquery-public-data.noaa_gsod.gsod1940` ) WHERE max != 9999.9 # code for missing data ORDER BY max DESC The same query using a wildcard table is much more concise: #standardSQL SELECT max, ROUND((max-32)*5/9,1) celsius, mo, da, year FROM `bigquery-public-data.noaa_gsod.gsod19*` WHERE max != 9999.9 # code for missing data AND _TABLE_SUFFIX BETWEEN '29' AND '40' ORDER BY max DESC Wildcard tables support native BigQuery storage only. You cannot use wildcards when querying an external table or a view. Querying sets of tables using wildcard tablesWildcard tables enable you to query several tables concisely. For example, a public dataset hosted by BigQuery, the NOAA Global Surface Summary of the Day Weather Data, contains a table for each year from 1929 through the present that all share the common prefix To query a group of tables that share a common prefix, use the table wildcard symbol (*) after the table prefix in your
Filtering selected tables using _TABLE_SUFFIXTo restrict a query so that it scans
only a specified set of tables, use the The
The corresponding For example, to filter for the maximum temperature in the years 1940 and 1944, use the values
Using However, filters on
As another example, the following query limits the scan based on the first filter condition,
As a workaround, you can perform two separate queries instead; for example: First query:
Second query:
These example queries use the Scanning a range of tables using _TABLE_SUFFIXTo scan a range of tables, use the
Scanning a range of ingestion-time partitioned tables using _PARTITIONTIMETo scan a range of ingestion-time partitioned tables, use the
Querying all tables in a datasetTo scan all tables in a dataset, you can use an empty
prefix and the table wildcard, which means that the
With an empty prefix, the
Note, however, that longer prefixes generally perform better. For more information, see Best practices. Query execution detailsSchema used for query evaluationIn order to execute a Google Standard SQL query that uses a wildcard table, BigQuery
automatically infers the schema for that table. BigQuery uses the schema for the most recently created table that matches the wildcard as the schema for the wildcard table. Even if you restrict the number of tables that you want to use from the wildcard table using the If a column from the inferred schema doesn't exist in a matched table, then BigQuery
returns If the schema is inconsistent across the tables matched by the wildcard query, then BigQuery returns an error. This is the case when the columns of the matched tables have different data types, or when the columns which are not present in all of the matched tables cannot be assumed to have a null value. Best practices
For best practices for controlling costs in BigQuery, see Controlling costs in BigQuery What's next
What is query with multiple tables?world multi-tables. UNION combines queries; multi-tables combine tables. With multi-tables you can easily combine tables if they have the same columns and then run queries against the resulting table. With UNION , queries can be run against the individual tables before they are joined into one table by the UNION .
Which clause is valid to query data from multiple tables?Answer: B. Equijoin is one of the types of joins which is the most common and simple technique for joining more than one tables. Equijoins are also called simple joins or inner joins. Equijoin involve primary key and foreign key.
Can we use multiple tables in update query?It is possible to join two or more tables in an UPDATE query.
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