GreptimeDB MySQL Protocol SHOW DATABASES Compatibility Issue

[jmmc-tools]

What type of bug is this?

Incorrect result

What subsystems are affected?

Other

Minimal reproduce step

Current Behavior (GreptimeDB):

SHOW DATABASES;

+---------+
| Schemas |
+---------+
| public  |
+---------+

Expected Behavior (MySQL Standard):

SHOW DATABASES;

+----------+
| Database |
+----------+
| public   |
+----------+

What did you expect to see?

SHOW DATABASES;

+---------+
| Schemas | ← Following standard MYSQL protocol specification : column should be | Database |
+---------+
| public |
+---------+

It's

MySQL Protocol Specification

• URL: https://dev.mysql.com/doc/refman/8.3/en/show-databases.html
• Evidence: MySQL Reference Manual specifies column name as Database
• Citation: "SHOW DATABASES lists the databases on the MySQL server host... The output displays only those databases for which you have some kind of privilege"
• Standard Column Name: Database (confirmed in MariaDB docs at https://mariadb.com/docs/server/reference/sql-statements/administrative-sql-statements/show/show-databases showing output with | Database |)

3. MySQL Information Schema Standard

• URL: https://dev.mysql.com/doc/refman/8.3/en/information-schema.html
• INFORMATION_SCHEMA.SCHEMATA Table: Contains SCHEMA_NAME column (not Schemas)
• Evidence: Standard metadata tables use singular column names per database entry

What did you see instead?

Error Trace

JDBC connection fails:
```
ERROR 1064 [42000]: ERROR: Failed to describe statement
```

This is only one example, but column names in other metadata queries (such as SHOW TABLES) could also be affected if they do not follow the MySQL specification. As a result, JDBC connectors using the MySQL driver fail to retrieve metadata correctly.

What operating system did you use?

helm greptimedb-cluster repo

What version of GreptimeDB did you use?

1.0.0-beta.1

Relevant log output and stack trace

[killme2008]

Thank you for your feedback.

From our perspective, most MySQL tools query the information_schema database to retrieve metadata such as databases, tables, and columns etc., while SHOW statements are typically used for administration by command-line tools like mysql.

I have previously(and some users are using) used JDBC with the MySQL driver for inserts and queries, and everything worked as expected. I’m therefore curious about the scenario in which you encountered this error. Could you share sample code or concrete examples?

[killme2008]

E.G.

I just wrote a simple java JDBC example:

import java.sql.*;

public class GreptimeDBExample {
    public static void main(String[] args) throws Exception {
        String url = "jdbc:mysql://localhost:4002/public";
        String user = "";
        String password = "";

        try (Connection conn = DriverManager.getConnection(url, user, password)) {
            // Create table
            String createTable = "CREATE TABLE IF NOT EXISTS sensor_data (" +
                "ts TIMESTAMP TIME INDEX, " +
                "sensor_name STRING PRIMARY KEY, " +
                "temperature DOUBLE, " +
                "is_active BOOLEAN)";
            conn.createStatement().execute(createTable);
            System.out.println("Table created.");

            // Insert data
            String insert = "INSERT INTO sensor_data (ts, sensor_name, temperature, is_active) VALUES (?, ?, ?, ?)";
            try (PreparedStatement ps = conn.prepareStatement(insert)) {
                ps.setTimestamp(1, new Timestamp(System.currentTimeMillis()));
                ps.setString(2, "sensor_1");
                ps.setDouble(3, 25.5);
                ps.setBoolean(4, true);
                ps.executeUpdate();
                System.out.println("Data inserted.");
            }

            // Query data
            ResultSet rs = conn.createStatement().executeQuery("SELECT * FROM sensor_data");
            while (rs.next()) {
                System.out.printf("ts=%s, name=%s, temp=%.2f, active=%b%n",
                    rs.getTimestamp("ts"), rs.getString("sensor_name"),
                    rs.getDouble("temperature"), rs.getBoolean("is_active"));
            }
        }
    }
}

Use the 8.0 JDBC driver:

curl -L -o mysql-connector.jar "https://repo1.maven.org/maven2/com/mysql/mysql-connector-j/8.0.33/mysql-connector-j-8.0.33.jar"

Looks good:

javac GreptimeDBExample.java && java -cp ".:mysql-connector.jar" GreptimeDBExample

Table created.
Data inserted.
ts=2025-11-22 00:59:39.189, name=sensor_1, temp=25.50, active=true
ts=2025-11-22 00:59:56.97, name=sensor_1, temp=25.50, active=true
ts=2025-11-22 01:01:07.176, name=sensor_1, temp=25.50, active=true

The data in the mysql:

mysql> SELECT * FROM sensor_data;
+----------------------------+-------------+-------------+-----------+
| ts                         | sensor_name | temperature | is_active |
+----------------------------+-------------+-------------+-----------+
| 2025-11-22 00:59:39.189000 | sensor_1    |        25.5 |         1 |
| 2025-11-22 00:59:56.970000 | sensor_1    |        25.5 |         1 |
| 2025-11-22 01:01:07.176000 | sensor_1    |        25.5 |         1 |
+----------------------------+-------------+-------------+-----------+
3 rows in set (0.02 sec)

[jmmc-tools]

I need integrate with Starrocks engine using JDBC External Catalog

CREATE EXTERNAL CATALOG jdbc1
PROPERTIES
(
"type"="jdbc",
"user"="root",
"password"="changeme",
"jdbc_uri"="jdbc:mysql://127.0.0.1:3306",
"driver_url"="https://repo1.maven.org/maven2/mysql/mysql-connector-java/8.0.28/mysql-connector-java-8.0.28.jar",
"driver_class"="com.mysql.cj.jdbc.Driver"
);

The external catalog was created successfully, so StarRocks can manage any MySQL server in remote mode (as long as the user has sufficient privileges).

I followed the official docs , but when running SHOW DATABASES, StarRocks always returns the error message mentioned in my previous post.

While investigating issues related to JDBC, I noticed that StarRocks is very strict about the MySQL protocol, especially regarding column names.

I think using GreptimeDB together with StarRocks could be a powerful combination, since both engines provide complementary features. Maybe GreptimeDB could adapt its metadata responses to improve integration with StarRocks.

[killme2008]

@jmmc-tools Got it—that makes sense.

Thanks, that’s helpful. I think we can adjust the column names in the show statements.

[killme2008]

These issues can be easily fixed by modifying the schema at:

greptimedb/src/query/src/sql.rs

Line 531 in 2783a52

pub async fn show_tables(

etc.
Contributions are welcome.

[kenwoodjw]

Please assign to me, I give a try

[killme2008]

Please assign to me，I give a try

Thanks!