PostgreSQL Select

Fetches data from a PostgreSQL database by providing a table name.

Overview

This Snap allows you to fetch data from a database by providing a table name and configuring the connection. The Snap produces the records from the database on its output view which can then be processed by a downstream Snap.

JSON paths can be used in a query and will have values from an incoming document substituted into the query. However, documents missing values for a given JSON path will be written to the Snap's error view. After a query is executed, the query's results are merged into the incoming document overwriting any existing keys' values. The original document is output if there are no results from the query.

Queries produced by the Snap have an equivalent format:

SELECT * FROM [table] WHERE [where clause] ORDER BY [ordering] LIMIT [limit] OFFSET [offset]

If more powerful functionality is desired, then the Execute Snap should be used.

Prerequisites

A valid PostgreSQL Account with the required permissions.

Support and Limitations

Known issue: The SQL statement will return a PGObject when returning non-standard types. You must use the Execute Snap in these cases.

Warning: Non-standard types include standard PostgreSQL extensions such as JSON or XML, types defined in third party extensions such as PostGIS, or types defined via CREATE TYPE color AS ENUM (RED, GREEN, BLUE).

Snap views

Type Description Examples of upstream and downstream Snaps
Input This Snap has at most one document input view. If the input view is defined, then the where clause can substitute incoming values for a given expression (in such as to use it as a lookup).
Output This Snap has one output view by default and produces one document for each row in the table. A second view can be added to dump out the metadata for the table as a document. The metadata document can then be fed into the second input view of PostgreSQL Insert Snap so that the table is created in PostgreSQL with a similar schema as the source table.
Learn more about Error handling.

Snap settings

Note: Learn about the common controls in the Snap settings dialog.
Field/Field set Type Description
Label

String

 Required. Specify a unique name for the Snap. Modify this to be more appropriate, especially if more than one of the same Snaps is in the pipeline.

Default value: PostgreSQL - Select

Example: Select Employees
Schema name

String

 The database schema name. Selecting a schema filters the Table name list to show only those tables within the selected schema. The property is suggestible and will retrieve available database schemas during suggest values.

Default value: N/A
Table name

String

 Required. Name of the table to execute a select query on.

Example: people

Default value: N/A
Where clause

String/Expression

 Where clause of the select statement. This supports document value substitution (such as $person.firstname will be substituted with the value found in the incoming document at the path).

Examples:

Without using expressions

Using expressions

  • "EMPNO=$EMPNO and ENAME=$EMPNAME"
  • email = $email
  • emp=$emp
  • "emp='" + $emp + "'"
  • "EMPNO=" + $EMPNO + " and ENAME='" + $EMPNAME+ "'"
Warning: Using expressions that join strings together to create SQL queries or conditions has a potential SQL injection risk and is hence unsafe. Ensure that you understand all implications and risks involved before using concatenation of strings with '=' Expression enabled.
Order by: Column names

String

 Enter in the columns in the order in which you want to order by. The default database sort order will be used.

Example: name, email
Limit offset

Integer

 The starting row from where the result set should begin.

Example: 10

Default value: N/A
Limit rows

Integer

 Number of rows to limit from the query.

Example: 10

Default value: N/A
Output fields

String

 Enter or select output field names for SQL SELECT statement. To select all fields, leave it at default.

Example: email, address, first, last

Default value: N/A
Fetch Output Fields In Schema

Checkbox

 If selected, the Snap fetches only the fields specified in the Output fields property. The Snap validates these fields against the database schema before executing the query. This option is useful when you want to retrieve a subset of columns from a table.

Default value: Not selected
Pass through

Checkbox

 If checked, the input document will be passed through to the output view under the key 'original'.

Default value: Selected
Ignore empty result

Checkbox

 If selected, no document will be written to the output view when a SELECT operation does not produce any result. If this property is not selected and the Pass through property is selected, the input document will be passed through to the output view.

Default value: Not selected
Number of retries

Integer/Expression

 Specifies the maximum number of attempts to be made to receive a response. The request is terminated if the attempts do not result in a response.
Note: If the value is larger than 0, the Snap first downloads the target file into a temporary local file. If any error occurs during the download, the Snap waits for the time specified in the Retry interval and attempts to download the file again from the beginning. When the download is successful, the Snap streams the data from the temporary file to the downstream Pipeline. All temporary local files are deleted when they are no longer needed. Ensure that the local drive has sufficient free disk space to store the temporary local file.

Example: 3

Default value: 0
Retry interval (seconds)

Integer/Expression

 Specifies the time interval between two successive retry requests. A retry happens only when the previous attempt resulted in an exception.

Example: 10

Default value: 1
Auto commit

Dropdown list

 Select one of the options for this property to override the state of the Auto commit property on the account. The Auto commit at the Snap-level has three values: True, False, and Use account setting. The expected functionality for these modes are:
  • True - The Snap will execute with auto-commit enabled regardless of the value set for Auto commit in the Account used by the Snap.
  • False - The Snap will execute with auto-commit disabled regardless of the value set for Auto commit in the Account used by the Snap.
  • Use account setting - The Snap will execute with Auto commit property value inherited by the Account used by the Snap.

Default value: False
Match data types

Checkbox

 Conditional. This property applies only when the Output fields property is provided with any field value(s).

If this property is selected, the Snap tries to match the output data types same as when the Output fields property is empty (SELECT * FROM ...). The output preview would be in the same format as the one when SELECT * FROM is implied and all the contents of the table are displayed.

Default value: Not selected
Staging mode

Dropdown list

 Required when the value in the Number of retries field is greater than 0.

Specify the location from the following options to store input documents between retries:

  • In memory: The query results are stored in the Snaplex memory. If the query is too large to fit in the memory space, it may cause the Snap to fail, choose the On disk option.
  • On disk: The query results are stored on the disk in a temporary (tmp) directory that is managed by the SnapLogic platform. This directory is deleted automatically when the Snap terminates.
Snap Execution

Dropdown list

Choose one of the three modes in which the Snap executes. Available options are:

  • Validate & Execute: Performs limited execution of the Snap and generates a data preview during pipeline validation. Subsequently, performs full execution of the Snap (unlimited records) during pipeline runtime.
  • Execute only: Performs full execution of the Snap during pipeline execution without generating preview data.
  • Disabled: Disables the Snap and all Snaps that are downstream from it.

Default value: Execute only

Example: Validate & Execute