# H2

<web-summary>
Use Kotlin DataFrame to query H2 databases via JDBC — read tables, run SQL queries, or fetch result sets directly.
</web-summary>

<card-summary>
Connect to H2 databases in Kotlin DataFrame and load data using simple JDBC configurations.
</card-summary>

<link-summary>
Read from H2 databases in Kotlin DataFrame using built-in SQL reading methods.
</link-summary>


Kotlin DataFrame supports reading from an [H2](https://www.h2database.com/html/main.html) database using JDBC.

Requires the [`dataframe-jdbc` module](Modules.md#dataframe-jdbc),
which is included by default in the general [`dataframe` artifact](Modules.md#dataframe-general)
and in [`%use dataframe`](SetupKotlinNotebook.md#integrate-kotlin-dataframe) for Kotlin Notebook.

You’ll also need [the official H2 JDBC driver](https://www.h2database.com/html/main.html):

<tabs>
<tab title="Gradle project">

```kotlin
dependencies {
    implementation("com.h2database:h2:$version")
}
```

</tab>
<tab title="Kotlin Notebook">


```kotlin
USE {
    dependencies("com.h2database:h2:$version")
}
```

</tab>
</tabs>

The actual Maven Central driver version could be found
[here](https://mvnrepository.com/artifact/com.h2database/h2).

## Read

[`DataFrame`](DataFrame.md) can be loaded from a database in several ways:  
a user can read data from a SQL table by given name ([`readSqlTable`](readSqlDatabases.md)),  
as a result of a user-defined SQL query ([`readSqlQuery`](readSqlDatabases.md)),  
or from a given `ResultSet` ([`readResultSet`](readSqlDatabases.md)).  
It is also possible to load all data from non-system tables, each into a separate `DataFrame` ([`readAllSqlTables`](readSqlDatabases.md)).

See [](readSqlDatabases.md) for more details.

### H2 Compatibility Modes

When working with H2 database, the library automatically detects the compatibility mode from the connection.
If no `MODE` is specified in the JDBC URL, the default `Regular` mode is used.
H2 supports the following compatibility modes: `MySQL`, `PostgreSQL`, `MSSQLServer`, `MariaDB`, and `Regular`.

```kotlin
import org.jetbrains.kotlinx.dataframe.io.DbConnectionConfig
import org.jetbrains.kotlinx.dataframe.api.*

// Basic H2 connection (uses Regular mode by default)

val url = "jdbc:h2:mem:testDatabase"
val username = "sa"
val password = ""

val dbConfig = DbConnectionConfig(url, username, password)

val tableName = "Customer"

val df = DataFrame.readSqlTable(dbConfig, tableName)
```

```kotlin
import org.jetbrains.kotlinx.dataframe.io.DbConnectionConfig
import org.jetbrains.kotlinx.dataframe.api.*

// H2 with PostgreSQL compatibility mode

val postgresUrl = "jdbc:h2:mem:testDatabase;MODE=PostgreSQL"
val username = "sa"
val password = ""

val postgresConfig = DbConnectionConfig(postgresUrl, username, password)

val tableName = "Customer"

val dfPostgres = DataFrame.readSqlTable(postgresConfig, tableName)
```