How to export BigQuery table schema as DDL - google-cloud-platform

Question

I need to create BigQuery table with the same schema as in existing one.
In standard MySql there is SHOW CREATE TABLE, is there something similar for BigQuery?

Answer 1

SELECT
table_name, ddl
FROM
`bigquery-public-data`.census_bureau_usa.INFORMATION_SCHEMA.TABLES;
https://cloud.google.com/blog/topics/developers-practitioners/spring-forward-bigquery-user-friendly-sql

Answer 2

Nothing similar to the SHOW CREATE TABLE from MySQL, but it is possible with the use of UDFs to generate the DDL statements of your tables in a dataset...
Use the following script and make sure to replace 'mydataset' with yours. You can even add a WHERE predicate to output only specific table DDL
Copy the output of the desired table and paste it in a new Compose Query Window and give it a new table name!
CREATE TEMP FUNCTION MakePartitionByExpression(
column_name STRING, data_type STRING
) AS (
IF(
column_name = '_PARTITIONTIME',
'DATE(_PARTITIONTIME)',
IF(
data_type = 'TIMESTAMP',
CONCAT('DATE(', column_name, ')'),
column_name
)
)
);
CREATE TEMP FUNCTION MakePartitionByClause(
columns ARRAY<STRUCT<column_name STRING, data_type STRING, is_nullable STRING, is_partitioning_column STRING, clustering_ordinal_position INT64>>
) AS (
IFNULL(
CONCAT(
'PARTITION BY ',
(SELECT MakePartitionByExpression(column_name, data_type)
FROM UNNEST(columns) WHERE is_partitioning_column = 'YES'),
'\n'),
''
)
);
CREATE TEMP FUNCTION MakeClusterByClause(
columns ARRAY<STRUCT<column_name STRING, data_type STRING, is_nullable STRING, is_partitioning_column STRING, clustering_ordinal_position INT64>>
) AS (
IFNULL(
CONCAT(
'CLUSTER BY ',
(SELECT STRING_AGG(column_name, ', ' ORDER BY clustering_ordinal_position)
FROM UNNEST(columns) WHERE clustering_ordinal_position IS NOT NULL),
'\n'
),
''
)
);
CREATE TEMP FUNCTION MakeNullable(data_type STRING, is_nullable STRING)
AS (
IF(not STARTS_WITH(data_type, 'ARRAY<') and is_nullable = 'NO', ' NOT NULL', '')
);
CREATE TEMP FUNCTION MakeColumnList(
columns ARRAY<STRUCT<column_name STRING, data_type STRING, is_nullable STRING, is_partitioning_column STRING, clustering_ordinal_position INT64>>
) AS (
IFNULL(
CONCAT(
'(\n',
(SELECT STRING_AGG(CONCAT(' ', column_name, ' ', data_type, MakeNullable(data_type, is_nullable)), ',\n')
FROM UNNEST(columns)),
'\n)\n'
),
''
)
);
CREATE TEMP FUNCTION MakeOptionList(
options ARRAY<STRUCT<option_name STRING, option_value STRING>>
) AS (
IFNULL(
CONCAT(
'OPTIONS (\n',
(SELECT STRING_AGG(CONCAT(' ', option_name, '=', option_value), ',\n') FROM UNNEST(options)),
'\n)\n'),
''
)
);
WITH Components AS (
SELECT
CONCAT('`', table_catalog, '.', table_schema, '.', table_name, '`') AS table_name,
ARRAY_AGG(
STRUCT(column_name, data_type, is_nullable, is_partitioning_column, clustering_ordinal_position)
ORDER BY ordinal_position
) AS columns,
(SELECT ARRAY_AGG(STRUCT(option_name, option_value))
FROM mydataset.INFORMATION_SCHEMA.TABLE_OPTIONS AS t2
WHERE t.table_name = t2.table_name) AS options
FROM mydataset.INFORMATION_SCHEMA.TABLES AS t
LEFT JOIN mydataset.INFORMATION_SCHEMA.COLUMNS
USING (table_catalog, table_schema, table_name)
WHERE table_type = 'BASE TABLE'
GROUP BY table_catalog, table_schema, t.table_name
)
SELECT
CONCAT(
'CREATE OR REPLACE TABLE ',
table_name,
'\n',
MakeColumnList(columns),
MakePartitionByClause(columns),
MakeClusterByClause(columns),
MakeOptionList(options))
FROM Components
For more info check -> Getting table metadata using INFORMATION_SCHEMA https://cloud.google.com/bigquery/docs/information-schema-tables

Answer 3

... to create BigQuery table with the same schema as in existing one
You can use below "trick" with your new table as destination (trick here is in using WHERE FALSE which makes below query free of cost with 0 rows in output while preserving schema)
#standardSQL
SELECT *
FROM `project.dataset.existing_table`
WHERE FALSE
Or you can use above statement in CTAS (CREATE TABLE AS SELECT) type of DDL