added Go example

examples/simple_query_in_go/.gitignore

@@ -0,0 +1,2 @@
+go.sum
+simple_query

examples/simple_query_in_go/go.mod

@@ -0,0 +1,31 @@
+module example/simple_query
+
+go 1.19
+
+require (
+	cloud.google.com/go/bigquery v1.44.0
+	google.golang.org/api v0.103.0
+)
+
+require (
+	cloud.google.com/go v0.105.0 // indirect
+	cloud.google.com/go/compute v1.12.1 // indirect
+	cloud.google.com/go/compute/metadata v0.2.1 // indirect
+	cloud.google.com/go/iam v0.7.0 // indirect
+	github.com/golang/groupcache v0.0.0-20200121045136-8c9f03a8e57e // indirect
+	github.com/golang/protobuf v1.5.2 // indirect
+	github.com/google/go-cmp v0.5.9 // indirect
+	github.com/google/uuid v1.3.0 // indirect
+	github.com/googleapis/enterprise-certificate-proxy v0.2.0 // indirect
+	github.com/googleapis/gax-go/v2 v2.7.0 // indirect
+	go.opencensus.io v0.24.0 // indirect
+	golang.org/x/net v0.0.0-20221014081412-f15817d10f9b // indirect
+	golang.org/x/oauth2 v0.0.0-20221014153046-6fdb5e3db783 // indirect
+	golang.org/x/sys v0.0.0-20220728004956-3c1f35247d10 // indirect
+	golang.org/x/text v0.4.0 // indirect
+	golang.org/x/xerrors v0.0.0-20220907171357-04be3eba64a2 // indirect
+	google.golang.org/appengine v1.6.7 // indirect
+	google.golang.org/genproto v0.0.0-20221117204609-8f9c96812029 // indirect
+	google.golang.org/grpc v1.50.1 // indirect
+	google.golang.org/protobuf v1.28.1 // indirect
+)

examples/simple_query_in_go/main.go

@@ -0,0 +1,87 @@
+/*  Cardano on BigQuery
+
+    example: simple query
+*/
+
+
+/*
+authenticate: `gcloud auth application-default login`
+prepare: `go mod tidy -v`
+compile: `go build`
+run: `go run . --epoch_no 321`
+ or: `./simple_query -epoch_no 321`
+*/
+
+package main
+
+import (
+	"context"
+	"flag"
+	"fmt"
+	"log"
+
+	"cloud.google.com/go/bigquery"
+	"google.golang.org/api/iterator"
+)
+
+func main() {
+
+	epoch_no := flag.Int("epoch_no", 251, "Indicate the epoch number for which you want to query its last block.")
+	flag.Parse()
+	if *epoch_no < 0 { log.Fatal("wrong epoch number specified.") }
+
+	ctx := context.Background()
+
+	// the GCP/BigQuery project id
+	projectID := "blockchain-analytics-392322"
+
+	bqclient, err := bigquery.NewClient(ctx, projectID)
+	if err != nil { log.Fatalf("bigquery.NewClient: %v", err) }
+	defer bqclient.Close()
+
+	rows, err := runQuery(ctx, bqclient, *epoch_no)
+	if err != nil { log.Fatalf("run query: %v", err) }
+
+	if err := printResults(rows); err != nil { log.Fatalf("print results: %v",err) }
+}
+
+func runQuery(ctx context.Context, client *bigquery.Client, p_epoch_no int) (*bigquery.RowIterator, error) {
+	query := client.Query(
+		`SELECT epoch_no, slot_no, block_time, block_size, tx_count,
+		        sum_tx_fee, script_count, sum_script_size, pool_hash
+		 FROM ` + "`cardano_mainnet.block`" + `
+		 WHERE epoch_no = ` + fmt.Sprintf("%d",p_epoch_no) + `
+		 ORDER BY slot_no DESC LIMIT 1;`)
+	return query.Read(ctx)
+}
+
+type Block struct {
+	EpochNo     int64  `bigquery:"epoch_no"`
+	SlotNo      int64  `bigquery:"slot_no"`
+	BlockTime   bigquery.NullDateTime `bigquery:"block_time"`
+	BlockSize   int64  `bigquery:"block_size"`
+	TxCount     int64  `bigquery:"tx_count"`
+	SumTxFee    int64  `bigquery:"sum_tx_fee"`
+	ScriptCount int64  `bigquery:"script_count"`
+	ScriptSize  int64  `bigquery:"sum_script_size"`
+	PoolHash    string  `bigquery:"pool_hash"`
+}
+func block2String(b *Block) string {
+	return fmt.Sprintf("epoch: %d, slot: %d, timestamp: %v, block sz: %d, tx count: %d, fees: %d, scripts: %d/%d bytes, pool: %v",
+					   b.EpochNo, b.SlotNo, b.BlockTime, b.BlockSize, b.TxCount, b.SumTxFee, b.ScriptCount, b.ScriptSize, b.PoolHash)
+}
+
+func printResults(iter *bigquery.RowIterator) error {
+	for {
+		var row Block
+		err := iter.Next(&row)
+		if err == iterator.Done {
+			return nil
+		}
+		if err != nil {
+			return fmt.Errorf("error iterating through results: %w", err)
+		}
+
+		fmt.Println(block2String(&row))
+	}
+}