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[FLINK-36221] Add CAST ... AS ... documentations #3596

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[FLINK-36221] Add CAST ... AS ... documentations #3596

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[FLINK-36221] Add `CAST ... AS ...` documentations
yuxiqian Sep 5, 2024
4d1a2f0
explain cryptic arguments
yuxiqian Oct 11, 2024
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17 changes: 17 additions & 0 deletions docs/content.zh/docs/core-concept/transform.md
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Expand Up @@ -153,6 +153,23 @@ Flink CDC uses [Calcite](https://calcite.apache.org/) to parse expressions and [
| COALESCE(value1 [, value2]*) | coalesce(Object... objects) | Returns the first argument that is not NULL.If all arguments are NULL, it returns NULL as well. The return type is the least restrictive, common type of all of its arguments. The return type is nullable if all arguments are nullable as well. |
| IF(condition, true_value, false_value) | condition ? true_value : false_value | Returns the true_value if condition is met, otherwise false_value. E.g., IF(5 > 3, 5, 3) returns 5. |

## Casting Functions

You can use `CAST( <EXPR> AS <TYPE> )` syntax to convert the type of expressions. Possible conversion paths are:
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| Source Type | Target Type | Notes |
|-------------------------------------|-------------|--------------------------------------------------------------------------------------------|
| ANY | STRING | All types can be cast to STRING. |
| NUMERIC, STRING | BOOLEAN | Any non-zero numerics will be evaluated to `TRUE`. |
| NUMERIC | BYTE | Value must be in the range of Byte (-128 ~ 127). |
| NUMERIC | SHORT | Value must be in the range of Short (-32768 ~ 32767). |
| NUMERIC | INTEGER | Value must be in the range of Integer (-2147483648 ~ 2147483647). |
| NUMERIC | LONG | Value must be in the range of Long (-9223372036854775808 ~ 9223372036854775807). |
| NUMERIC | FLOAT | Value must be in the range of Float (1.40239846e-45f ~ 3.40282347e+38f). |
| NUMERIC | DOUBLE | Value must be in the range of Double (4.94065645841246544e-324 ~ 1.79769313486231570e+308) |
| NUMERIC | DECIMAL | Value must be in the range of BigDecimal(10, 0). |
| STRING, TIMESTAMP_TZ, TIMESTAMP_LTZ | TIMESTAMP | String type value must be a valid `ISO_LOCAL_DATE_TIME` string. |

# Example
## Add computed columns
Evaluation expressions can be used to generate new columns. For example, if we want to append two computed columns based on the table `web_order` in the database `mydb`, we may define a transform rule as follows:
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17 changes: 17 additions & 0 deletions docs/content/docs/core-concept/transform.md
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Original file line number Diff line number Diff line change
Expand Up @@ -153,6 +153,23 @@ Flink CDC uses [Calcite](https://calcite.apache.org/) to parse expressions and [
| COALESCE(value1 [, value2]*) | coalesce(Object... objects) | Returns the first argument that is not NULL.If all arguments are NULL, it returns NULL as well. The return type is the least restrictive, common type of all of its arguments. The return type is nullable if all arguments are nullable as well. |
| IF(condition, true_value, false_value) | condition ? true_value : false_value | Returns the true_value if condition is met, otherwise false_value. E.g., IF(5 > 3, 5, 3) returns 5. |

## Casting Functions

You can use `CAST( <EXPR> AS <TYPE> )` syntax to convert the type of expressions. Possible conversion paths are:

| Source Type | Target Type | Notes |
|-------------------------------------|-------------|--------------------------------------------------------------------------------------------|
| ANY | STRING | All types can be cast to STRING. |
| NUMERIC, STRING | BOOLEAN | Any non-zero numerics will be evaluated to `TRUE`. |
| NUMERIC | BYTE | Value must be in the range of Byte (-128 ~ 127). |
| NUMERIC | SHORT | Value must be in the range of Short (-32768 ~ 32767). |
| NUMERIC | INTEGER | Value must be in the range of Integer (-2147483648 ~ 2147483647). |
| NUMERIC | LONG | Value must be in the range of Long (-9223372036854775808 ~ 9223372036854775807). |
| NUMERIC | FLOAT | Value must be in the range of Float (1.40239846e-45f ~ 3.40282347e+38f). |
| NUMERIC | DOUBLE | Value must be in the range of Double (4.94065645841246544e-324 ~ 1.79769313486231570e+308) |
| NUMERIC | DECIMAL | Value must be in the range of BigDecimal(10, 0). |
| STRING, TIMESTAMP_TZ, TIMESTAMP_LTZ | TIMESTAMP | String type value must be a valid `ISO_LOCAL_DATE_TIME` string. |

# Example
## Add computed columns
Evaluation expressions can be used to generate new columns. For example, if we want to append two computed columns based on the table `web_order` in the database `mydb`, we may define a transform rule as follows:
Expand Down
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