Add 3 examples in playground SQL transform, schema transform and Composite Combine

[razvanculea]

3 simple examples of applying multiple combiners on the input PCollection (Min,Max,Sum).

3 different ways of achieving this in Beam

• SQL transform, using the powerful SQL syntax
• Schema transformations, leveraging schemas and Group.byFilelds
• Composed Combiners, same results without the need to use Rows or Schema transforms and with full control over the combiner logic

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[razvanculea]

@damondouglas this blog post will explain how to apply multiple combiners to an input PColl in different ways with Beam and link to these 3 examples

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Reminder, please take a look at this pr: @damondouglas

[razvanculea]

assign to next reviewer

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R: @kennknowles for label java.

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[Abacn]

Use "Beam SQL" per https://github.com/apache/beam/blob/master/playground/categories.yaml#L33

[Abacn]

Thanks, just had a minor comment

[Abacn]

Please add the new subproject to https://github.com/apache/beam/blob/master/build.gradle.kts#L254 to include the build in precommit test

[Abacn]

The error message is:

* What went wrong:
Execution failed for task ':examples:java:sql:analyzeClassesDependencies'.
> Dependency analysis found issues.
  unusedDeclaredArtifacts
   - beam.sdks.java.extensions:google-cloud-platform-core:2.65.0-SNAPSHOT@jar
   - beam.sdks.java.extensions:ml:2.65.0-SNAPSHOT@jar
   - beam.sdks.java.extensions:python:2.65.0-SNAPSHOT@jar
   - beam.sdks.java.io:google-cloud-platform:2.65.0-SNAPSHOT@jar
   - beam.sdks.java:managed:2.65.0-SNAPSHOT@jar
   - com.fasterxml.jackson.core:jackson-annotations:2.15.4@jar
   - com.fasterxml.jackson.core:jackson-core:2.15.4@jar
   - com.fasterxml.jackson.core:jackson-databind:2.15.4@jar
   - com.google.api-client:google-api-client:2.0.0@jar
   - com.google.api.grpc:proto-google-cloud-bigtable-v2:2.56.0@jar
   - com.google.api.grpc:proto-google-cloud-datastore-v1:0.118.1@jar
   - com.google.api.grpc:proto-google-cloud-language-v1:2.61.0@jar
   - com.google.apis:google-api-services-bigquery:v2-rev20250313-2.0.0@jar
   - com.google.apis:google-api-services-pubsub:v1-rev20220904-2.0.0@jar
   - com.google.auth:google-auth-library-credentials:1.33.1@jar
   - com.google.auth:google-auth-library-oauth2-http:1.33.1@jar
   - com.google.cloud.bigdataoss:util:2.2.26@jar
   - com.google.cloud.datastore:datastore-v1-proto-client:2.27.1@jar
   - com.google.code.gson:gson:2.10.1@jar
   - com.google.http-client:google-http-client:1.46.3@jar
   - com.google.oauth-client:google-oauth-client:1.34.1@jar
   - com.google.protobuf:protobuf-java:4.29.4@jar
   - commons-io:commons-io:2.16.1@jar
   - joda-time:joda-time:2.10.14@jar
   - org.apache.beam:beam-vendor-grpc-1_69_0:0.1@jar
   - org.apache.beam:beam-vendor-guava-32_1_2-jre:0.1@jar
   - org.apache.commons:commons-csv:1.8@jar
   - org.apache.commons:commons-lang3:3.14.0@jar
   - org.apache.httpcomponents:httpclient:4.5.13@jar
   - org.apache.httpcomponents:httpcore:4.4.14@jar
   - org.apache.kafka:kafka-clients:2.4.1@jar

need to clean up build.gradle

[Abacn]

Thank you!