[receiver/mysql] client, convert NULL to int64 (open-telemetry#34411)

**Description:** <Describe what has changed.>
bug fix, receiver/mysql client.go raise error when the TABLE_ROWS column
is NULL,
fix it in the SQL query, convert the NULL to 0.

**Link to tracking Issue:** <Issue number if applicable>

open-telemetry#34195
**Testing:** <Describe what testing was performed and which tests were
added.>
run command "make test" in the receiver/mysqlreceiver, all the test case
passed.
**Documentation:** <Describe the documentation added.>

---------

Signed-off-by: Jian Li <[email protected]>

Author: knarfli

.chloggen/mysqlreceiver-convert-null-to-int64.yaml

@@ -0,0 +1,27 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: bug_fix
+
+# The name of the component, or a single word describing the area of concern, (e.g. filelogreceiver)
+component: mysqlreceiver
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: mysql client raise error when the TABLE_ROWS column is NULL, convert NULL to int64
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [34195]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext:
+
+# If your change doesn't affect end users or the exported elements of any package,
+# you should instead start your pull request title with [chore] or use the "Skip Changelog" label.
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: [user]

receiver/mysqlreceiver/client.go

@@ -243,8 +243,11 @@ func (c *mySQLClient) getInnodbStats() (map[string]string, error) {
 
 // getTableStats queries the db for information_schema table size metrics.
 func (c *mySQLClient) getTableStats() ([]TableStats, error) {
-	query := "SELECT TABLE_SCHEMA, TABLE_NAME, TABLE_ROWS, " +
-		"AVG_ROW_LENGTH, DATA_LENGTH, INDEX_LENGTH " +
+	query := "SELECT TABLE_SCHEMA, TABLE_NAME, " +
+		"COALESCE(TABLE_ROWS, 0) as TABLE_ROWS, " +
+		"COALESCE(AVG_ROW_LENGTH, 0) as AVG_ROW_LENGTH, " +
+		"COALESCE(DATA_LENGTH, 0) as DATA_LENGTH, " +
+		"COALESCE(INDEX_LENGTH, 0) as  INDEX_LENGTH " +
 		"FROM information_schema.TABLES " +
 		"WHERE TABLE_SCHEMA NOT in ('information_schema', 'sys');"
 	rows, err := c.client.Query(query)