join_simple.go

// heavily borrowed from Rosetta Code example
package main

import "fmt"

type row map[string]interface{}

var (
	tableA = []row{
		row{"name": "Jonah", "age": 27},
		row{"name": "Alan", "age": 18},
		row{"name": "Glory", "age": 28},
		row{"name": "Popeye", "age": 18},
		row{"name": "Alan", "age": 28},
	}

	tableB = []row{
		row{"name": "Jonah", "fear": "Whales"},
		row{"name": "Jonah", "fear": "Spiders"},
		row{"name": "Alan", "fear": "Ghosts"},
		row{"name": "Alan", "fear": "Zombies"},
		row{"name": "Glory", "fear": "Buffy"},
	}
)

func main() {
	Join(tableA, tableB, "name")
}

func Join(t1, t2 []row, on string) {
	// hash phase
	h := map[string][]interface{}{}
	for _, r := range t1 {
		key := r[on].(string)
		val := fmt.Sprintf("%v", r["age"])
		h[key] = append(h[key], val)
	}

	// join phase
	for _, r := range t2 {
		key := r[on].(string)
		for k, v := range r {
			if k != on {
				val := fmt.Sprintf("%v", v)
				for _, a := range h[key] {
					fmt.Println(key, a, val)
				}
			}
		}
	}
}