# Table to Table SQL and DDL files
## :map: Overview
A SQL workflow is a sequence of tasks that feed tables in parallel or sequentially.
A workflow can be composed of the following task types:
* SQL task ("sql"): instructions to load, merge and reorganize data.
* Table creation task ("create\_gbq\_table"): instructions to create a destination table.
* Table copy task ("copy\_gbq\_table"): instructions to duplicate a table (provided in the [data operation configuration file](https://docs.tailer.ai/data-pipeline-operations/transform-data-with-tables-to-tables/tables-to-tables-configuration-file)).
## :oil: SQL tasks
SQL tasks are steps of the workflow. Each SQL task is defined with a .sql file that contains the query. You can write the queries directly in the query editor of [BigQuery](https://console.cloud.google.com/bigquery) and then save them to .sql files.
{% hint style="info" %}
The file can contain a SQL query or a SQL script (like assertions or expectations).
{% endhint %}
{% hint style="info" %}
The name of the SQL file should be the same as the SQL task.
{% endhint %}
Example:
```sql
SELECT
customer_id,
optin,
cast(creation_date as date) as creation_date
FROM `referential.customers`
QUALIFY ROW_NUMBER() OVER(dedup_pk) = 1
WINDOW dedup_pk as (
PARTITION BY customer_id
ORDER BY update_date desc, import_date desc, tlr_ingestion_timestamp_utc desc
)
```
## :new: Table creation tasks
Once the SQL queries are ready, you need to use one or several DDL files to create the destination BigQuery tables that will contain the output data.
### DDL Example
```json
{
"bq_table_description": "Describe the content of the table. The description will be attached to the table bigquery Metadata",
"bq_table_schema": [
{
"name": "field_date",
"type": "DATE",
"description": "Describe the field_date"
},
{
"name": "field_2",
"type": "STRING",
"description": "Describe the field_2"
},
{
"name": "field_3",
"type": "INTEGER",
"description": "Describe the field_3",
"mode": "REQUIRED"
}
],
"bq_table_clustering_fields": ["field_2", "field_3"]
"bq_table_timepartitioning_field": "field_date",
"bq_table_timepartitioning_type": "MONTH",
"bq_table_timepartitioning_expiration_ms": "86400000",
"bq_table_timepartitioning_require_partition_filter": false
}
```
### **DDL Parameters**
| Parameter | Description |
| ------------------------------------------------------------------------------------------------------------------ | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| bq\_table\_description
type: string
mandatory
| Description of the BigQuery table. |
| bq\_table\_schema
type: array
mandatory
| BigQuery table schema. It contains a list of fields corresponding to the number of columns it will contain.
Each field described has three attributes:
|
| bq\_table\_clustering\_fields
type: array
optional
| List of fields used when clustering is enabled.
The table data will be automatically organized based on the contents of the fields you specify. Their order determines the sort order of the data.
If this parameter is set, time partitioning will be automatically enabled on the table. If you don't set partitioning parameters, default values will be used.
|
| bq\_table\_timepartitioning\_field
type: string
optional
| If this parameter is set, the table will be partitioned by this field.
If not, the table will be partitioned by pseudo column \_PARTITIONTIME.
The field must be a top-level TIMESTAMP or DATE field. Its mode must be NULLABLE or REQUIRED.
(Refer to BigQuery documentation for more information.)
Note: You can set this parameter to a field that equals to DATE(''). Then, if you relaunch an execution with a partition, and if default\_write\_disposition is set to "WRITE\_APPEND" in the JSON configuration file, Tailer will check if the corresponding partition already exists in the table:
- If it does, it will delete it, and replace it with the current execution data.
- If not, it will add them.
|
| bq\_table\_timepartitioning\_type
type: string
optional
| Sets the partition type. Use one of the following values: "HOUR", "DAY", "MONTH" or "YEAR".
If not present, default is "DAY".
|
| bq\_table\_timepartitioning\_expiration\_ms
type: integer
optional
| Number of milliseconds for which to keep the storage for a partition.
(Refer to BigQuery documentation for more information.)
|
| bq\_table\_timepartitioning\_require\_partition\_filter
type: boolean
optional
| If set to true, queries over the partitioned table require a partition filter that can be used for partition elimination to be specified.
(Refer to BigQuery documentation for more information.)
|
### DDL Data Types
Tailer Platform supports the following data types.
#### Numeric types
| Name | Description |
| --------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| `int64` | Integers are numeric values that do not have fractional components.
They range from -9,223,372,036,854,775,808 to 9,223,372,036,854,775,807.
|
| `float64` | Floating point values are approximate numeric values with fractional components. |
| `numeric` | This data type represents decimal values with 38 decimal digits of precision and 9 decimal digits of scale. (Precision is the number of digits that the number contains. Scale is how many of these digits appear after the decimal point.)
It is particularly useful for financial calculations.
|
#### Boolean type
| Name | Description |
| --------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| `boolean` | This data type supports the `true`, `false`, and `null` values. It can perform some basic conversions, such as `'true'`, `'True'`, `True`, or 1 becoming `true`. |
#### String type
| Name | Description |
| -------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| `string` | Variable-length character data.
When converting data from string to a different data type, makes sure to use safe\_cast when you're unsure about the data quality.
|
#### Bytes type
| Name | Description |
| ------- | ------------------------------------------------------------------------------------------------------------------ |
| `bytes` | Variable-length binary data. This data type is rarely used but can be useful for characters with unusual encoding. |
#### Time types
{% hint style="info" %}
Only the `date`, `datetime` and `timestamp` data types (not `time`) allow table partitioning.
{% endhint %}
{% hint style="info" %}
Time zone management being difficult with BigQuery, prefer the UTC format.
{% endhint %}
| Name | Description |
| ----------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| `date` | This data type represents a calendar date. It includes the year, month, and day. |
| `time` | This data type represents a time, as might be displayed on a watch, independent of a specific date. It includes the hour, minute, second, and subsecond. |
| `datetime` | This data type represents a date and time, as they might be displayed on a calendar or clock. It includes the year, month, day, hour, minute, second, and subsecond. |
| `timestamp` | This data type represents an absolute point in time, with microsecond precision. |
## :aquarius: Table copy tasks
If necessary, you can duplicate an existing table using a table copy task, for example to share the contents of a table with a partner inside their own dataset. Although it would be possible to use an SQL script with **SELECT \***, a copy task is more efficient. The parameters set in the JSON configuration file are sufficient, no specific file is required for this type of task.