kou commented on code in PR #707:
URL: https://github.com/apache/arrow-adbc/pull/707#discussion_r1204933000
##########
c/driver/postgresql/statement.cc:
##########
@@ -649,17 +649,27 @@ AdbcStatusCode PostgresStatement::ExecuteQuery(struct
ArrowArrayStream* stream,
return ADBC_STATUS_INVALID_STATE;
}
- // 1. Execute the query with LIMIT 0 to get the schema
+ // 1. Prepare the query to get the schema
{
// TODO: we should pipeline here and assume this will succeed
- std::string schema_query = "SELECT * FROM (" + query_ + ") AS ignored
LIMIT 0";
- PGresult* result =
- PQexecParams(connection_->conn(), query_.c_str(), /*nParams=*/0,
- /*paramTypes=*/nullptr, /*paramValues=*/nullptr,
- /*paramLengths=*/nullptr, /*paramFormats=*/nullptr,
kPgBinaryFormat);
- if (PQresultStatus(result) != PGRES_TUPLES_OK) {
- SetError(error, "%s%s", "[libpq] Query was: ", schema_query.c_str());
- SetError(error, "%s%s", "[libpq] Failed to execute query: could not
infer schema: ",
+ PGresult* result = PQprepare(connection_->conn(), /*stmtName=*/"",
query_.c_str(),
+ /*nParams=*/0, nullptr);
+ if (PQresultStatus(result) != PGRES_COMMAND_OK) {
+ SetError(error, "%s%s", "[libpq] Query was: ", query_.c_str());
+ SetError(error, "%s%s",
+ "[libpq] Failed to execute query: could not infer schema:
failed to "
+ "prepare query: ",
+ PQerrorMessage(connection_->conn()));
Review Comment:
How about unifying these `SetError()`s to one `SetError()`?
It seems that the current `SetError()` implementation discards the previous
error message. (`[libpq] Query was: ${query}` is discarded.)
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