#320: hardcoded the size of MySQL data type TEXT (#323)

* #320: hardcoded the size of MySQL data type TEXT because the driver can return an incorrect value.
* #320: fixed review findings and adjusted documentation for MySQL dialect

doc/dialects/athena.md

@@ -49,7 +49,7 @@ The SQL statement below creates the adapter script, defines the Java class that
 ```sql
 CREATE OR REPLACE JAVA ADAPTER SCRIPT ADAPTER.JDBC_ADAPTER AS
     %scriptclass com.exasol.adapter.RequestDispatcher;
-    %jar /buckets/<BFS service>/<bucket>/virtualschema-jdbc-adapter-dist-3.1.1.jar;
+    %jar /buckets/<BFS service>/<bucket>/virtualschema-jdbc-adapter-dist-3.1.2.jar;
     %jar /buckets/<BFS service>/<bucket>/AthenaJDBC42-<JDBC driver version>.jar;
 /
 ;

doc/dialects/aurora.md

@@ -62,7 +62,7 @@ The SQL statement below creates the adapter script, defines the Java class that
 ```sql
 CREATE OR REPLACE JAVA ADAPTER SCRIPT ADAPTER.JDBC_ADAPTER AS
     %scriptclass com.exasol.adapter.RequestDispatcher;
-    %jar /buckets/<BFS service>/<bucket>/virtualschema-jdbc-adapter-dist-3.1.1.jar;
+    %jar /buckets/<BFS service>/<bucket>/virtualschema-jdbc-adapter-dist-3.1.2.jar;
     %jar /buckets/<BFS service>/<bucket>/postgresql-<JDBC driver version>.jar;
 /
 ```

doc/dialects/bigquery.md

@@ -33,7 +33,7 @@ List all the JAR files from Magnitude Simba JDBC driver.
 ```sql
 CREATE JAVA ADAPTER SCRIPT SCHEMA_FOR_VS_SCRIPT.ADAPTER_SCRIPT_BIGQUERY AS
     %scriptclass com.exasol.adapter.RequestDispatcher;
-    %jar /buckets/<BFS service>/<bucket>/virtualschema-jdbc-adapter-dist-3.1.1.jar;
+    %jar /buckets/<BFS service>/<bucket>/virtualschema-jdbc-adapter-dist-3.1.2.jar;
     %jar /buckets/<BFS service>/<bucket>/GoogleBigQueryJDBC42.jar;
     ...
     ...

doc/dialects/db2.md

@@ -56,7 +56,7 @@ The SQL statement below creates the adapter script, defines the Java class that
 ```sql
 CREATE OR REPLACE JAVA ADAPTER SCRIPT ADAPTER.JDBC_ADAPTER AS
   %scriptclass com.exasol.adapter.RequestDispatcher;
-  %jar /buckets/<BFS service>/<bucket>/virtualschema-jdbc-adapter-dist-3.1.1.jar;
+  %jar /buckets/<BFS service>/<bucket>/virtualschema-jdbc-adapter-dist-3.1.2.jar;
   %jar /buckets/<BFS service>/<bucket>/db2jcc4.jar;
   %jar /buckets/<BFS service>/<bucket>/db2jcc_license_cu.jar;
 /
@@ -68,7 +68,7 @@ CREATE OR REPLACE JAVA ADAPTER SCRIPT ADAPTER.JDBC_ADAPTER AS
 ```sql
 CREATE OR REPLACE JAVA ADAPTER SCRIPT ADAPTER.JDBC_ADAPTER AS
   %scriptclass com.exasol.adapter.RequestDispatcher;
-  %jar /buckets/<BFS service>/<bucket>/virtualschema-jdbc-adapter-dist-3.1.1.jar;
+  %jar /buckets/<BFS service>/<bucket>/virtualschema-jdbc-adapter-dist-3.1.2.jar;
   %jar /buckets/<BFS service>/<bucket>/db2jcc4.jar;
   %jar /buckets/<BFS service>/<bucket>/db2jcc_license_cu.jar;
   %jar /buckets/<BFS service>/<bucket>/db2jcc_license_cisuz.jar;

doc/dialects/exasol.md

@@ -18,7 +18,7 @@ The SQL statement below creates the adapter script, defines the Java class that
 ```sql
 CREATE JAVA ADAPTER SCRIPT ADAPTER.JDBC_ADAPTER AS
     %scriptclass com.exasol.adapter.RequestDispatcher;
-    %jar /buckets/<BFS service>/<bucket>/virtualschema-jdbc-adapter-dist-3.1.1.jar;
+    %jar /buckets/<BFS service>/<bucket>/virtualschema-jdbc-adapter-dist-3.1.2.jar;
 /
 ```
 

doc/dialects/hive.md

@@ -47,7 +47,7 @@ The SQL statement below creates the adapter script, defines the Java class that
 ```sql
 CREATE OR REPLACE JAVA ADAPTER SCRIPT ADAPTER.JDBC_ADAPTER AS
   %scriptclass com.exasol.adapter.RequestDispatcher;
-  %jar /buckets/<BFS service>/<bucket>/jars/virtualschema-jdbc-adapter-dist-3.1.1.jar;
+  %jar /buckets/<BFS service>/<bucket>/jars/virtualschema-jdbc-adapter-dist-3.1.2.jar;
   %jar /buckets/<BFS service>/<bucket>/jars/HiveJDBC41.jar;
 /
 ```

doc/dialects/impala.md

@@ -47,7 +47,7 @@ The SQL statement below creates the adapter script, defines the Java class that
 ```sql
 CREATE OR REPLACE JAVA ADAPTER SCRIPT ADAPTER.JDBC_ADAPTER AS
   %scriptclass com.exasol.adapter.RequestDispatcher;
-  %jar /buckets/<BFS service>/<bucket>/virtualschema-jdbc-adapter-dist-3.1.1.jar;
+  %jar /buckets/<BFS service>/<bucket>/virtualschema-jdbc-adapter-dist-3.1.2.jar;
   %jar /buckets/<BFS service>/<bucket>/ImpalaJDBC41.jar;
 /
 ;

doc/dialects/mysql.md

@@ -43,15 +43,15 @@ Upload the latest available release of [Virtual Schema JDBC Adapter](https://git
 Then create a schema to hold the adapter script.
 
 ```sql
-CREATE SCHEMA ADAPTER;
+CREATE SCHEMA SCHEMA_FOR_VS_SCRIPT;
 ```
 
 The SQL statement below creates the adapter script, defines the Java class that serves as entry point and tells the UDF framework where to find the libraries (JAR files) for Virtual Schema and database driver.
 
 ```sql
-CREATE OR REPLACE JAVA ADAPTER SCRIPT ADAPTER.JDBC_ADAPTER AS
+CREATE OR REPLACE JAVA ADAPTER SCRIPT SCHEMA_FOR_VS_SCRIPT.ADAPTER_SCRIPT_MYSQL AS
     %scriptclass com.exasol.adapter.RequestDispatcher;
-    %jar /buckets/<BFS service>/<bucket>/virtualschema-jdbc-adapter-dist-3.1.1.jar;
+    %jar /buckets/<BFS service>/<bucket>/virtualschema-jdbc-adapter-dist-3.1.2.jar;
     %jar /buckets/<BFS service>/<bucket>/mysql-connector-java-<version>.jar;
 /
 ;
@@ -62,7 +62,7 @@ CREATE OR REPLACE JAVA ADAPTER SCRIPT ADAPTER.JDBC_ADAPTER AS
 Define the connection to MySQL as shown below.
 
 ```sql
-CREATE OR REPLACE CONNECTION MYSQL_CONNECTION
+CREATE OR REPLACE CONNECTION MYSQL_JDBC_CONNECTION
 TO 'jdbc:mysql://<host>:<port>/'
 USER '<user>'
 IDENTIFIED BY '<password>';
@@ -74,14 +74,56 @@ Below you see how a MySQL Virtual Schema is created. Use CATALOG_NAME property t
 
 ```sql
 CREATE VIRTUAL SCHEMA <virtual schema name>
-    USING ADAPTER.JDBC_ADAPTER
+    USING SCHEMA_FOR_VS_SCRIPT.ADAPTER_SCRIPT_MYSQL
     WITH
     SQL_DIALECT = 'MYSQL'
-    CONNECTION_NAME = 'MYSQL_CONNECTION'
+    CONNECTION_NAME = 'MYSQL_JDBC_CONNECTION'
     CATALOG_NAME = '<database name>';
 ```
 
-## Data Types Mapping and Limitations
-
-- `TIME` is casted to `TIMESTAMP` with a format `1970-01-01 hh:mm:ss`.   
-- Unsupported data types: `BINARY`, `VARBINARY`, `BLOB`, `TINYBLOB`, `MEDIUMBLOB`, `LONGBLOB`.
+## Data Types Conversion
+
+MySQL Data Type    | Supported | Converted Exasol Data Type| Known limitations
+-------------------|-----------|---------------------------|-------------------
+BOOLEAN            |  ✓        | BOOLEAN                   | 
+BIGINT             |  ✓        | DECIMAL                   | 
+BINARY             |  ×        |                           | 
+BIT                |  ✓        | BOOLEAN                   | 
+BLOB               |  ×        |                           | 
+CHAR               |  ✓        | CHAR                      | 
+DATE               |  ✓        | DATE                      | 
+DATETIME           |  ✓        | TIMESTAMP                 | 
+DECIMAL            |  ✓        | DECIMAL                   |  
+DOUBLE             |  ✓        | DOUBLE PRECISION          | 
+ENUM               |  ✓        | CHAR                      | 
+FLOAT              |  ✓        | DOUBLE PRECISION          |  
+INT                |  ✓        | DECIMAL                   | 
+LONGBLOB           |  ×        |                           | 
+LONGTEXT           |  ✓        | VARCHAR(2000000)          | 
+MEDIUMBLOB         |  ×        |                           | 
+MEDIUMINT          |  ✓        | DECIMAL                   | 
+MEDIUMTEXT         |  ✓        | VARCHAR(2000000)          | 
+SET                |  ✓        | CHAR                      | 
+SMALLINT           |  ✓        | DECIMAL                   | 
+TEXT               |  ✓        | VARCHAR(65535)            | The size of the column is always 65535.*
+TINYBLOB           |  ×        |                           | 
+TINYINT            |  ✓        | DECIMAL                   | 
+TINYTEXT           |  ✓        | VARCHAR                   | 
+TIME               |  ✓        | TIMESTAMP                 | Casted to `TIMESTAMP` with a format `1970-01-01 hh:mm:ss`.  
+TIMESTAMP          |  ✓        | TIMESTAMP                 | 
+VARBINARY          |  ×        |                           | 
+VARCHAR            |  ✓        | VARCHAR                   | 
+YEAR               |  ✓        | DATE                      |
+
+* The tested versions of MySQL Connector JDBC Driver return the column's size depending on the charset and its collation. 
+As the real data in a MySQL table can sometimes exceed the size that we get from the JDBC driver, we set the size for all TEXT columns to 65535 characters.  
+
+If you need to use currently unsupported data types or find a way around known limitations, please, create a github issue in the [VS repository](https://github.com/exasol/virtual-schemas/issues).
+
+## Testing information
+
+In the following matrix you find combinations of JDBC driver and dialect version that we tested.
+
+Virtual Schema Version| Big Query Version   | Driver Name              | Driver Version 
+----------------------|---------------------|--------------------------|------------------------
+ 3.1.1                | MySQL 8.0.19        | MySQL Connector          |  8.0.17 

doc/dialects/oracle.md

@@ -48,7 +48,7 @@ The SQL statement below creates the adapter script, defines the Java class that
 ```sql
 CREATE JAVA ADAPTER SCRIPT ADAPTER.JDBC_ADAPTER AS
   %scriptclass com.exasol.adapter.RequestDispatcher;
-  %jar /buckets/<BFS service>/<bucket>/virtualschema-jdbc-adapter-dist-3.1.1.jar;
+  %jar /buckets/<BFS service>/<bucket>/virtualschema-jdbc-adapter-dist-3.1.2.jar;
   %jar /buckets/<BFS service>/<bucket>/ojdbc<JDBC driver version>.jar;
 /
 ;

doc/dialects/postgresql.md

@@ -24,7 +24,7 @@ The SQL statement below creates the adapter script, defines the Java class that
 ```sql
 CREATE OR REPLACE JAVA ADAPTER SCRIPT ADAPTER.JDBC_ADAPTER AS
   %scriptclass com.exasol.adapter.RequestDispatcher;
-  %jar /buckets/<BFS service>/<bucket>/virtualschema-jdbc-adapter-dist-3.1.1.jar;
+  %jar /buckets/<BFS service>/<bucket>/virtualschema-jdbc-adapter-dist-3.1.2.jar;
   %jar /buckets/<BFS service>/<bucket>/postgresql-<version>.jar;
 /
 ```

doc/dialects/redshift.md

@@ -51,7 +51,7 @@ The SQL statement below creates the adapter script, defines the Java class that
 ```sql
 CREATE OR REPLACE JAVA ADAPTER SCRIPT ADAPTER.JDBC_ADAPTER AS
     %scriptclass com.exasol.adapter.RequestDispatcher;
-    %jar /buckets/<BFS service>/<bucket>/virtualschema-jdbc-adapter-dist-3.1.1.jar;
+    %jar /buckets/<BFS service>/<bucket>/virtualschema-jdbc-adapter-dist-3.1.2.jar;
     %jar /buckets/<BFS service>/<bucket>/RedshiftJDBC42-<JDBC driver version>.jar;
 /
 ;

doc/dialects/saphana.md

@@ -47,7 +47,7 @@ The SQL statement below creates the adapter script, defines the Java class that
 ```sql
 CREATE JAVA ADAPTER SCRIPT ADAPTER.JDBC_ADAPTER AS
      %scriptclass com.exasol.adapter.RequestDispatcher;
-     %jar /buckets/<BFS service>/<bucket>/virtualschema-jdbc-adapter-dist-3.1.1.jar;
+     %jar /buckets/<BFS service>/<bucket>/virtualschema-jdbc-adapter-dist-3.1.2.jar;
      %jar /buckets/<BFS service>/<bucket>/ngdbc-<JDBC driver version>.jar;
 /
 ;

doc/dialects/sql_server.md

@@ -24,7 +24,7 @@ The SQL statement below creates the adapter script, defines the Java class that
 ```sql
 CREATE OR REPLACE JAVA ADAPTER SCRIPT ADAPTER.JDBC_ADAPTER AS
   %scriptclass com.exasol.adapter.RequestDispatcher;
-  %jar /buckets/<BFS service>/<bucket>/virtualschema-jdbc-adapter-dist-3.1.1.jar;
+  %jar /buckets/<BFS service>/<bucket>/virtualschema-jdbc-adapter-dist-3.1.2.jar;
   %jar /buckets/<BFS service>/<bucket>/jtds.jar;
 /
 ```

doc/dialects/sybase.md

@@ -29,7 +29,7 @@ The SQL statement below creates the adapter script, defines the Java class that
 ```sql
 CREATE OR REPLACE JAVA ADAPTER SCRIPT ADAPTER.JDBC_ADAPTER AS
   %scriptclass com.exasol.adapter.RequestDispatcher;
-  %jar /buckets/<BFS service>/<bucket>/virtualschema-jdbc-adapter-dist-3.1.1.jar;
+  %jar /buckets/<BFS service>/<bucket>/virtualschema-jdbc-adapter-dist-3.1.2.jar;
   %jar /buckets/<BFS service>/<bucket>/jtds-<version>.jar;
 /
 ```

doc/dialects/teradata.md

@@ -47,7 +47,7 @@ The SQL statement below creates the adapter script, defines the Java class that
 ```sql
 CREATE OR REPLACE JAVA ADAPTER SCRIPT ADAPTER.JDBC_ADAPTER AS
   %scriptclass com.exasol.adapter.RequestDispatcher;
-  %jar /buckets/<BFS service>/<bucket>/virtualschema-jdbc-adapter-dist-3.1.1.jar;
+  %jar /buckets/<BFS service>/<bucket>/virtualschema-jdbc-adapter-dist-3.1.2.jar;
   %jar /buckets/<BFS service>/<bucket>/terajdbc4.jar;
   %jar /buckets/<BFS service>/<bucket>/tdgssconfig.jar;
 /

doc/user-guide/user_guide.md

@@ -85,7 +85,7 @@ The SQL statement below creates the adapter script, defines the Java class that
 ```sql
 CREATE JAVA ADAPTER SCRIPT SCHEMA_FOR_VS_SCRIPT.JDBC_ADAPTER_SCRIPT AS
   %scriptclass com.exasol.adapter.RequestDispatcher;
-  %jar /buckets/your-bucket-fs/your-bucket/virtualschema-jdbc-adapter-dist-3.1.1.jar;
+  %jar /buckets/your-bucket-fs/your-bucket/virtualschema-jdbc-adapter-dist-3.1.2.jar;
   %jar /buckets/your-bucket-fs/your-bucket/<JDBC driver>.jar;
 /
 ```

pom.xml

@@ -7,7 +7,7 @@
     <version>${product.version}</version>
     <name>Virtual Schema JDBC Adapter</name>
     <properties>
-        <product.version>3.1.1</product.version>
+        <product.version>3.1.2</product.version>
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
         <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
         <java.version>11</java.version>

src/main/java/com/exasol/adapter/dialects/mysql/MySqlColumnMetadataReader.java

@@ -13,6 +13,9 @@
  * This class implements MySQL-specific reading of column metadata.
  */
 public class MySqlColumnMetadataReader extends BaseColumnMetadataReader {
+    private static final String TEXT_DATA_TYPE_NAME = "TEXT";
+    protected static final int TEXT_DATA_TYPE_SIZE = 65535;
+
     /**
      * Create a new instance of the {@link MySqlColumnMetadataReader}.
      *
@@ -32,8 +35,40 @@ public DataType mapJdbcType(final JdbcTypeDescription jdbcTypeDescription) {
             return DataType.createTimestamp(false);
         case Types.BINARY:
             return DataType.createUnsupported();
+        case Types.LONGVARCHAR:
+            return convertVarChar(jdbcTypeDescription);
         default:
             return super.mapJdbcType(jdbcTypeDescription);
         }
     }
+
+    private DataType convertVarChar(final JdbcTypeDescription jdbcTypeDescription) {
+        final int size = getVarcharSize(jdbcTypeDescription);
+        final int octetLength = jdbcTypeDescription.getByteSize();
+        final DataType.ExaCharset charset = (octetLength == size) ? DataType.ExaCharset.ASCII
+                : DataType.ExaCharset.UTF8;
+        if (size <= DataType.MAX_EXASOL_VARCHAR_SIZE) {
+            final int precision = getVarcharPrecision(size);
+            return DataType.createVarChar(precision, charset);
+        } else {
+            return DataType.createVarChar(DataType.MAX_EXASOL_VARCHAR_SIZE, charset);
+        }
+    }
+
+    private int getVarcharPrecision(int size) {
+        if (size == 0) {
+            return DataType.MAX_EXASOL_VARCHAR_SIZE;
+        } else {
+            return size;
+        }
+    }
+
+    private int getVarcharSize(final JdbcTypeDescription jdbcTypeDescription) {
+        final String typeName = jdbcTypeDescription.getTypeName();
+        if (typeName.equals(TEXT_DATA_TYPE_NAME)) {
+            return TEXT_DATA_TYPE_SIZE;
+        } else {
+            return jdbcTypeDescription.getPrecisionOrSize();
+        }
+    }
 }

src/test/java/com/exasol/adapter/dialects/IntegrationTestConstants.java

@@ -4,7 +4,7 @@
 
 public final class IntegrationTestConstants {
     public static final String INTEGRATION_TEST_CONFIGURATION_FILE_PROPERTY = "integrationtest.configfile";
-    public static final String VIRTUAL_SCHEMAS_JAR_NAME_AND_VERSION = "virtualschema-jdbc-adapter-dist-3.1.1.jar";
+    public static final String VIRTUAL_SCHEMAS_JAR_NAME_AND_VERSION = "virtualschema-jdbc-adapter-dist-3.1.2.jar";
     public static final Path PATH_TO_VIRTUAL_SCHEMAS_JAR = Path.of("target", VIRTUAL_SCHEMAS_JAR_NAME_AND_VERSION);
     public static final String SCHEMA_EXASOL = "SCHEMA_EXASOL";
     public static final String ADAPTER_SCRIPT_EXASOL = "ADAPTER_SCRIPT_EXASOL";

src/test/java/com/exasol/adapter/dialects/mysql/MySqlColumnMetadataReaderTest.java

@@ -1,5 +1,7 @@
 package com.exasol.adapter.dialects.mysql;
 
+import static com.exasol.adapter.dialects.mysql.MySqlColumnMetadataReader.TEXT_DATA_TYPE_SIZE;
+import static com.exasol.adapter.metadata.DataType.MAX_EXASOL_VARCHAR_SIZE;
 import static org.hamcrest.CoreMatchers.equalTo;
 import static org.hamcrest.MatcherAssert.assertThat;
 
@@ -33,4 +35,17 @@ void mapBinary() {
         final JdbcTypeDescription typeDescription = new JdbcTypeDescription(Types.BINARY, 0, 0, 10, "BINARY");
         assertThat(columnMetadataReader.mapJdbcType(typeDescription), equalTo(DataType.createUnsupported()));
     }
+
+    @Test
+    void mapText() {
+        final JdbcTypeDescription typeDescription = new JdbcTypeDescription(Types.LONGVARCHAR, 0, 16383, 10, "TEXT");
+        assertThat(columnMetadataReader.mapJdbcType(typeDescription).getSize(), equalTo(TEXT_DATA_TYPE_SIZE));
+    }
+
+    @Test
+    void mapMediumText() {
+        final JdbcTypeDescription typeDescription = new JdbcTypeDescription(Types.LONGVARCHAR, 0, 4194303, 10,
+                "MEDIUMTEXT");
+        assertThat(columnMetadataReader.mapJdbcType(typeDescription).getSize(), equalTo(MAX_EXASOL_VARCHAR_SIZE));
+    }
 }