If the error was associated with a specific constraint, the name of the constraint. Refer to fields listed above for the associated table or domain. (For this purpose, indexes are treated as constraints, even if they weren't created with constraint syntax.)
If the error was associated with a specific data type, the name of the data type.
Optional secondary error message carrying more detail about the problem. Might run to multiple lines.
File name of the source-code location where the error was reported.
Optional suggestion what to do about the problem. This is intended to differ from Detail in that it offers advice (potentially inappropriate) rather than hard facts. Might run to multiple lines.
this is defined the same as the position field, but it is used when the cursor position refers to an internally generated command rather than the one submitted by the client. The q field will always appear when this field appears.
Text of a failed internally-generated command. This could be, for example, a SQL query issued by a PL/pgSQL function.
Line number of the source-code location where the error was reported.
Primary human-readable error message. This should be accurate but terse (typically one line). Always present.
Decimal ASCII integer, indicating an error cursor position as an index into the original query string. The first character has index 1, and positions are measured in characters not bytes.
Name of the source-code routine reporting the error.
Field contents are ERROR, FATAL, or PANIC (in an error message), or WARNING, NOTICE, DEBUG, INFO, or LOG (in a notice message), or a localized translation of one of these. Always present.
Field contents are ERROR, FATAL, or PANIC (in an error message), or WARNING, NOTICE, DEBUG, INFO, or LOG (in a notice message). This is identical to the 'severity' field except that the contents are never localized. This is present only in messages generated by PostgreSQL versions 9.6 and later.
Context in which the error occurred. Presently this includes a call stack traceback of active procedural language functions and internally-generated queries. The trace is one entry per line, most recent first.
Contents of NoticeResponse or ErrorResponse messages. https://www.postgresql.org/docs/current/static/protocol-error-fields.html